Scaling up polarized RPE cell supernatant production on parylene membrane

Age-related macular degeneration (AMD), a leading cause of vision loss, primarily arises from the degeneration of retinal pigment epithelium (RPE) and photoreceptors. Current therapeutic options for dry AMD are limited. Encouragingly, cultured RPE cells on parylene-based biomimetic Bruch's membrane demonstrate characteristics akin to the native RPE layer. In this study, we cultivated human embryonic stem cell-derived polarized RPE (hESC-PRPE) cells on parylene membranes at both small- and large-scale settings, collecting conditioned supernatant, denoted as PRPE-SF. We conducted a comprehensive analysis of the morphology of the cultured hESC-RPE cells and the secreted growth factors in PRPE-SF. To evaluate the in vivo efficacy of these products, the product was administered via intravitreal injections of PRPE-SF in immunodeficient Royal College of Surgeons (iRCS) rats, a model for retinal degeneration. Our study not only demonstrated the scalability of PRPE-SF production while maintaining RPE cell phenotype but also showed consistent protein concentrations between small- and large-scale batches. We consistently identified 10 key factors in PRPE-SF, including BMP-7, IGFBP-2, IGFBP-3, IGFBP-4, IGFBP-6, MANF, PEDF, PDGF-AA, TGFβ1, and VEGF. Following intravitreal administration of PRPE-SF, we observed a significant increase in the thickness of the outer nuclear layer (ONL) and photoreceptor preservation in iRCS rats. Furthermore, correlation analysis revealed that IGFBP-3, IGFBP-4, MANF, PEDF, and TGFβ1 displayed positive associations with in vivo bioactivity, while GDF-15 exhibited a negative correlation. Overall, this study highlights the feasibility of scaling up PRPE-SF production on parylene membranes without compromising its essential constituents. The outcomes of PRPE-SF administration in an animal model of retinal degeneration present substantial potential for photoreceptor preservation. Moreover, the identification of candidate surrogate potency markers, showing strong positive associations with in vivo bioactivity, lays a solid foundation for the development of a promising therapeutic intervention for retinal degenerative diseases.

Reduction in Pappalysin-2 Levels and Lower IGF-I Bioavailability in Female Adolescents With Anorexia Nervosa

CONTEXT

Anorexia nervosa (AN) can cause severe undernutrition associated with alterations in the IGF axis. Pappalysins (PAPP-A, PAPP-A2) and stanniocalcins (STC-1, STC-2) modulate IGF binding-protein (IGFBP) cleavage and IGF bioavailability, but their implications in AN are unknown.

OBJECTIVE

We determined serum levels of PAPP-As and STCs in relationship with classical IGF axis parameters in female adolescents with AN and their association with nutritional status and secondary amenorrhea.

METHODS

Parameters of the IGF axis were determined in fasting serum samples of 68 female adolescents with AN at diagnosis and 62 sex- and age-matched controls. Standardized body mass index (BMI) and bone mineral density (BMD) were calculated.

RESULTS

Patients with AN had lower concentrations of total and free IGF-I, total IGFBP-3, acid-labile subunit (ALS), insulin, PAPP-A2, STC-1, and STC-2 and higher levels of IGF-II and IGFBP-2. Their free/total IGF-I ratio was decreased and the intact/total IGFBP-3 and -4 ratios increased. BMI was directly related to total IGF-I and intact IGFBP-3 and inversely with IGFBP-2 and intact IGFBP-4. Weight loss was directly correlated with intact IGFBP-4 and negatively with intact IGFBP-3, ALS, STC-2, and PAPP-A2 concentrations. BMD was directly related to intact IGFBP-3 and inversely with intact IGFBP-4 and PAPP-A2 levels. Patients with amenorrhea had lower levels of total IGF-I and IGFBP-3 than those with menses.

CONCLUSION

The reduction of PAPP-A2 in patients with AN may be involved in a decline in IGFBP cleavage, which could underlie the decrease in IGF-I bioavailability that is influenced by nutritional status and amenorrhea.

Circulating miR-4739 and IGFBP-4 Levels in Postmenopausal Women with Osteoporosis and Osteoporotic Vertebral Fracture

Objective

This study aimed to investigate the potential plasma miRNA-mRNA regulatory networks in postmenopausal women with osteoporosis (OP) and osteoporotic vertebral fracture (OVF).

Methods

The study employed a cross-sectional design, and the microarray dataset GSE93883 was acquired from the Gene Expression Omnibus (GEO) to assess plasma miRNA profiles in postmenopausal women with osteoporosis (OP) and osteoporotic vertebral fracture (OVF). Subsequently, plasma microRNA-4739 (miR-4739) and Insulin-like Growth Factor Binding Protein-4 (IGFBP-4) levels were validated in a well-defined cohort comprising 210 postmenopausal women. This cohort consisted of three distinct groups: healthy controls (HC, n = 70), OP patients (n = 70), and OVF patients (n = 70).

Results

Analysis of the GSE93883 dataset revealed a stepwise increase in four miRNAs (hsa-miR-4739, hsa-miR-4505, hsa-miR-4459, hsa-miR-665) in plasma samples from HC to OP patients to OVF patients. Conversely, plasma miR-4666a-3p showed a gradual decrease. We predicted six genes targeted by miR-4739 using six online databases. Plasma miR-4739 levels were significantly higher in OP and OVF patients compared to HC, especially in OVF patients. However, plasma IGFBP-4 exhibited an inverse pattern. Pearson analysis demonstrated a significant negative correlation between plasma miR-4739 and plasma IGFBP-4 in OP and OVF patients. Receiver operating characteristic (ROC) curve analysis of plasma miR-4739 yielded a sensitivity of 35.71% and specificity of 95.71% for predicting the presence of OP and a sensitivity of 71.43% and specificity of 95.71% for predicting OVF, with an AUC of 0.865. Moreover, the area under the curve (AUC) for IGFBP-4 was higher than that for plasma miR-4739 when differentiating OP patients from OVF patients.

Conclusions

Circulating miR-4739 and IGFBP-4 demonstrated a negative correlation in OP and OVF patients, suggesting their potential as diagnostic biomarkers for OP and OVF in the future.

Increased Levels of Circulating IGFBP4 and ANGPTL8 with a Prospective Role in Diabetic Nephropathy

Diabetic nephropathy (DN) is a complicated condition related to type 2 diabetes mellitus (T2D). ANGPTL8 is a hepatic protein highlighted as a risk factor for DN in patients with T2D; additionally, recent evidence from DN studies supports the involvement of growth hormone/IGF/IGF-binding protein axis constituents. The potential link between ANGPTL8 and IGFBPs in DN has not been explored before. Here, we assessed changes in the circulating ANGPTL8 levels in patients with DN and its association with IGFBP-1, -3, and -4. Our data revealed a significant rise in circulating ANGPTL8 in people with DN, 4443.35 ± 396 ng/mL compared to 2059.73 ± 216 ng/mL in people with T2D (p < 0.001). Similarly, levels of IGFBP-3 and -4 were significantly higher in people with DN compared to the T2D group. Interestingly, the rise in ANGPTL8 levels correlated positively with IGFBP-4 levels in T2DM patients with DN (p < 0.001) and this significant correlation disappeared in T2DM patients without DN. It also correlated positively with serum creatinine and negatively with the estimated glomerular filtration rate (eGFR, All < 0.05). The area under the curve (AUC) on receiver operating characteristic (ROC) analysis of the combination of ANGPTL8 and IGFBP4 was 0.76 (0.69-0.84), p < 0.001, and the specificity was 85.9%. In conclusion, our results showed a significant increase in ANGPTL8 in patients with DN that correlated exclusively with IGFBP-4, implicating a potential role of both proteins in the pathophysiology of DN. Our findings highlight the significance of these biomarkers, suggesting them as promising diagnostic molecules for the detection of diabetic nephropathy.

The Stanniocalcin-PAPP-A-IGFBP-IGF Axis

The pappalysin metalloproteinases, PAPP-A and PAPP-A2, have emerged as highly specific proteolytic enzymes involved in the regulation of insulin-like growth factor (IGF) signaling. The only known pappalysin substrates are a subset of the IGF binding proteins (IGFBPs), which bind IGF-I or IGF-II with high affinity to antagonize receptor binding. Thus, by cleaving IGFBPs, the pappalysins have the potential to increase IGF bioactivity and hence promote IGF signaling. This is relevant both in systemic and local IGF regulation, in normal and several pathophysiological conditions. Stanniocalcin-1 and -2 were recently found to be potent pappalysin inhibitors, thus comprising the missing components of a complete proteolytic system, the stanniocalcin-PAPP-A-IGFBP-IGF axis. Here, we provide the biological context necessary for understanding the properties of this molecular network, and we review biochemical data, animal experiments, clinical data, and genetic data supporting the physiological operation of this branch as an important part of the IGF system. However, although in vivo data clearly illustrate its power, it is a challenge to understand its subtle operation, for example, multiple equilibria and inhibitory kinetics may determine how, where, and when the IGF receptor is stimulated. In addition, literally all of the regulatory proteins have suspected or known activities that are not directly related to IGF signaling. How such activities may integrate with IGF signaling is also important to address in the future.

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.

Studies on the mechanisms by which insulin-like growth factor (IGF) binding protein-4 (IGFBP-4) and IGFBP-5 modulate IGF actions in bone cells

The growth potentiating effects of the insulin-like growth factor (IGF)-I and IGF-II are modulated by a family of six insulin-like growth factor binding proteins (IGFBPs). Despite the similarity in amino acid sequences of the IGFBPs, their effects on the growth of bone cells differ. Studies on the molecular mechanisms for IGFBP-4 actions revealed that coincubation of bone cells with IGFBP-4 and 125I-IGF-I or 125I-IGF-II decreased the binding of both of these ligands in a dose-dependent manner. In addition, IGFBP-4 decreased the binding of IGF-I tracer to purified type I IGF receptor. These data in conjunction with data showing that IGFBP-4 had no effect on cell proliferation induced by analogs of IGF-I or IGF-II, which exhibited > 100-fold reduced affinity for binding to IGFBP-4 suggest that IGFBP-4 may inhibit IGF action by preventing the binding of ligand to its membrane receptor. In contrast to IGFBP-4, IGFBP-5 treatment increased the binding of IGF tracer to bone cells but did not increase the binding of 125I-IGF-I to type I IGF receptor. Studies on the mechanism by which IGFBP-5 increased the binding of 125I-IGF tracer to bone cells suggest that IGFBP-5 could facilitate IGF binding by a mechanism in which IGFBP-5 has cell surface binding sites independent of IGF receptors. These data in conjunction with the findings that IGFBP-5 potentiated cell proliferation even in the presence of those same IGF analogs that exhibited > 200-fold reduced affinity for binding to IGFBP-5, suggest that IGFBP-5 may in part stimulate bone cell proliferation by an IGF-independent mechanism involving IGFBP-5-specific cell surface binding sites.

Analysis of insulin-like growth factor binding proteins in the tammar wallaby, Macropus eugenii

The insulin-like growth factors (IGFs) are important regulators of growth and development in eutherian mammals. In this study we have analyzed circulating insulin-like growth factor binding proteins (IGFBPs) by Western ligand blotting (WLB) and neutral gel filtration, and hepatic IGFBP mRNA transcripts in the wallaby, Macropus eugenii, a marsupial in which the fetus is born at an immature stage compared to eutherian mammals. Plasma from male and female adults, lactating mothers, and pouch young contains an IGF binding species consisting of a 42- to 50-kDa doublet, 30, 28, 24, and approximately 200 kDa, as shown by WLB. This pattern of IGFBPs is very similar to that observed in human and sheep. Neutral gel filtration revealed IGF binding activity of molecular size 70-160 kDa. When electrophoresed under nonreducing, denaturing conditions, the 70- to 160-kDa IGF binding activity appeared as a 42- to 50-kDa doublet, indicating the presence of a high-molecular-weight circulating IGF binding complex. These properties are again analogous to those observed for eutherian IGFBPs. Northern analysis of total wallaby liver RNA detected transcripts of 1.8 kb for IGFBP-1 and 1.6 kb for IGFBP-2, the same as those observed in the sheep and rat. Transcripts of 3.2 kb were detected for IGFBP-4, larger than the major band of 2.6 kb observed for the sheep and rat. Transcripts representing wallaby IGFBP-3 mRNA were not detected using a rat IGFBP-3 cDNA probe. Circulating IGFBPs were analyzed in plasma from wallaby mothers and their pouch young. There were no changes in circulating IGFBPs in the wallaby mothers throughout lactation.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of insulin-like growth factor (IGF) binding protein-2 synthesis and degradation by platelet-derived growth factor and the IGFs is enhanced by serum deprivation in vascular smooth muscle cells

Growth factors such as platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF-I) stimulated proliferation and migration of vascular smooth muscle cells (SMC). IGF-I bioactivity is modulated by high-affinity binding proteins (IGFBP) which are important regulators of these processes. Porcine vascular SMC synthesize IGFBP-2 and IGFBP-4 in vitro. In the present study, levels of IGFBP-2 in conditioned media (CM) were increased approximately 1.6 to 2.2-fold when cells were exposed to PDGF (20 ng/ml) or insulin (5 micrograms/ml) for 24 hr following a 24 hr incubation in serum-free media, or following a 72 hr exposure to either growth factor. Similar increases in IGFBP-2 mRNA levels were observed. Exposure of cells to PDGF for 24 hr without prior serum deprivation resulted in smaller (47 +/- 11%) increases in IGFBP-2 protein levels but failed to alter mRNA levels. IGF-I, FGF, TGF-beta and EGF failed to increase IGFBP-2 using either experimental paradigm. In contrast, IGFBP-2 protein levels were consistently decreased (75 +/- 14%) after 72 hr of exposure to IGF-II without corresponding decreases in IGFBP-2 mRNA levels. Immunoprecipitation of [35S]methionine-labeled IGFBP-2 indicated that this decrease was not due to a decrease in synthesis of IGFBP-2. Immunoblot analysis of CM from cells treated with IGF-II indicated that the decrease in intact protein corresponded with an increase in two non-IGF binding IGFBP-2 fragments of 22 and 14 kD. Increased abundance of these fragments was also observed following IGF-I exposure, although corresponding decreases in intact IGFBP-2 were not usually observed. The relative abundance of these fragments did not appear to be affected by treatment with PDGF or insulin. In contrast to IGFBP-2, regulation of the levels of IGFBP-4 in CM did not appear to be altered by serum deprivation. Insulin consistently increased IGFBP-4 mRNA and protein levels under all situations. PDGF tended to increase IGFBP-4 protein levels, although this effect was less consistent and not as great as the increase observed with insulin. Treatment with IGF-I or -II consistently decreased IGFBP-4 levels in CM but tended to increase their mRNA levels under all situations. These data indicate that insulin, PDGF, and the IGFs regulate both IGFBP-2 and IGFBP-4. While PDGF and insulin stimulate IGFBP-2 and 4 synthesis, the IGFs appear to activate protease(s) which regulate IGFBP-2 and -4 levels post-translationally.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin-like growth factor binding protein production in human follicular thyroid carcinoma cells

IGFs and IGF binding proteins (IGFBPs) appear to serve as regulators of non-malignant thyroid cells from several species, but little is known about their role in thyroid malignancy. We have examined IGFBP production and hormonal regulation in two human thyroid follicular carcinoma cell lines; FTC-133 line derived from a local tumor recurrence and FTC-236 cells from a tumor metastasis. Under basal conditions these cell lines produced IGFBP-3, IGFBP-4 and IGFBP-2. In both cell lines, EGF or TPA stimulated IGFBP-3 production while TSH or forskolin inhibited IGFBP-3 production and reduced the stimulation of IGFBP-3 seen with EGF or TPA. IGFBP-4 production was increased in the presence of TSH, forskolin, and EGF and was reduced by TPA. mRNA assessment revealed that IGFBP-3 mRNA, more abundant in FTC-236 than FTC-133 cells, increased in the presence of EGF or TPA, while IGFBP-4 mRNA content was increased in the presence of TSH, EGF, and forskolin. These results indicate that IGFBP production in human thyroid follicular carcinoma clones is under specific hormonal regulation. IGFBP-3 production is increased by dedifferentiation factors such as EGF and TPA and inhibited by TSH and forskolin, which enhance differentiated function. The highly specific regulation of IGFBP-3 and IGFBP-4 suggests a potential role for these peptides in modulating malignant thyroid growth.

Investigation into the potential physiological sources of rat milk IGF-I and IGF-binding proteins

We have previously reported the presence of IGF-I and IGF-binding proteins (IGFBP-2, -3 and -4) in rat milk. Herein, the potential sources of rat milk IGF-I and IGFBPs were investigated. Lactating dams (day 14 postpartum) were separated from their pups and injected intraperitoneally with 0.45 microCi 125I-IGF-I or 125I-IGFBP-3. After 3 h, serum and milk of rats receiving 125I-IGF-I contained 7642 +/- 3121 and 14,455 +/- 7837 c.p.m./ml respectively. Serum and milk of rats given 125I-IGFBP-3 contained 7232 +/- 1366 and 10,371 +/- 4091 c.p.m./ml respectively. Sephacryl S-200 gel filtration chromatography demonstrated that the 125I-IGF-I in both serum and milk was primarily in the 150 kDa IGF-binding complex, whereas the distribution of 125I-IGFBP-3 differed between serum and milk. In serum, most of the 125I-IGFBP-3 was in the 150 kDa fraction, while most 125I-IGFBP-3 in milk was in the 40 kDa fraction. Northern analysis of liver showed IGFBP-1 and -3 mRNA expression, with variable expression of IGFBP-2 and -4 mRNA. In contrast, mammary tissue expressed only IGFBP-2 and -4 mRNA, suggesting that these IGFBPs in milk may arise from de novo synthesis within the mammary gland. The lack of detectable IGFBP-3 mRNA in mammary tissue and the translocation of 125I-IGFBP-3 from the serum suggest that milk IGFBP-3 arises from the maternal circulation.

IGF, type I IGF receptor and IGF-binding protein mRNA expression in the developing mouse lung

The IGFs are important mitogens involved in lung growth and development. The regulation of IGF action depends not only on the expression of IGFs and IGF receptors, but also on the modulation of IGF activity by IGF-binding proteins (IGFBPs). In this study, we describe the mRNA expression of IGF-I, IGF-II, type I IGF receptor, IGFBP-2, IGFBP-4 and IGFBP-5 during mouse lung development as studied by in situ hybridization techniques. The IGF, type I IGF receptor and IGFBP-2, -4 and -5 genes were expressed in developing lung as early as embryonal day 12.5. Expression of IGFBPs-1, -3 and -6 was below detection. IGF and IGFBP-2 mRNAs were expressed both in mesenchymal and epithelial cells. Type I IGF receptor transcripts were also observed throughout the developing lung, with the exception of the epithelial cells of the bronchi after embryonal day 15. Furthermore, mRNA expression of IGFBPs-4 and -5 was noted in neighbouring cell types, and after embryonal day 15, co-expression of the type I IGF receptor and IGFBP-4 transcripts was detected. The observed expression patterns imply that the IGFBP-2, -4 and -5 genes are differentially regulated during embryonic development and suggest that each may have a discrete function. A possible role for IGFBPs-2, -4 and -5 is to participate in the regulation of cell-specific IGF responses during mouse lung development.

Characterization of insulin-like growth factor binding proteins (IGFBP) and regulation of IGFBP-4 in bone marrow stromal cells

Bone marrow stromal cells synthesize and secrete insulin-like growth factor (IGF)-I and IGF-binding proteins (IGFBP). IGFBPs may modulate the action of IGF-I or IGF-II on haemopoiesis. However, the specific IGFBPs produced by various stromal cell types have not been identified. We examined six different stromal phenotypes for IGFBP protein and IGFBP-1 to -6 mRNA expression. [125I]IGF-I ligand blot analysis of conditioned medium demonstrate different patterns of IGFBP secretion by each cell type. The most prominent IGFBPs were 24 and 29 kD species, consistent with IGFBP4 and IGFBP5, respectively. RNase protection assays demonstrate that, overall, stromal cells express IGFBP-2 to -6 mRNAs, with IGFBP4, IGFBP5 and IGFBP6 mRNAs predominating. Since agents that modulate cAMP levels may influence haemopoiesis via the release of stromal-derived cytokines, we determined the effect of forskolin, a cAMP agonist, on IGFBP4 expression in TC-1 cells. Forskolin (10(-5) M) up-regulated IGFBP4 mRNA and protein secretion in a time-dependent manner. These findings suggest that IGFBP-4, -5 and -6 released by stromal cells may be key modulators of the haemopoietic response to IGFs. Release of IGFBP4 by agents that increase cAMP may be an important mechanism involved in regulating IGF bioavailability in the marrow microenvironment.

Bone morphogenetic protein-2 inhibits the synthesis of insulin-like growth factor-binding protein-5 in bone cell cultures

Previous work from our laboratory indicated that bone morphogenetic protein-2 (BMP-2) enhances the synthesis of insulin-like growth factor-I (IGF-I) and IGF-II by skeletal cells. The activity of IGF-I and -II is regulated by six known IGF-binding proteins (IGFBPs). Although most IGFBP's inhibit the actions of IGF on bone growth, IGFBP-5 is stimulatory, and its synthesis correlates with changes in osteoblast cell growth. We tested the effects of BMP-2 on IGFBP-5 expression in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). Treatment of Ob cells with BMP-2 caused a time- and dose-dependent decrease in IGFBP-5 messenger RNA (mRNA) levels, as determined by Northern blot analysis. The effect was maximal after 24 h of treatment and occurred at BMP-2 concentrations of 0.03-3.3 nM. Treatment with BMP-2 for 24 h also decreased IGFBP-5 polypeptide levels in the extracellular matrix, as determined by Western blot analysis. The effects of BMP-2 on IGFBP-5 transcripts were independent of cell division, as they were observed in the presence and absence of hydroxyurea (1 mM). IGFBP-5 transcripts were barely detectable in the presence of the protein synthesis inhibitor cycloheximide at 3.6 microM, and further suppressive effects of BMP-2 on IGFBP-5 mRNA could not be determined. BMP-2 did not modify the decay of IGFBP-5 mRNA in transcriptionally arrested Ob cells. In addition, BMP-2 inhibited IGFBP-5 heterogeneous nuclear RNA, determined by reverse transcription-polymerase chain reaction, after 2-6 h of treatment, suggesting an inhibition of IGFBP-5 transcription or processing. In conclusion, BMP-2 inhibits IGFBP-5 expression in Ob cells through pathways that are independent of its mitogenic activity and through mechanisms that may involve decreased transcription or altered RNA processing.

Properties of an insulin-like growth factor-binding protein-4 protease that is secreted by smooth muscle cells

Smooth muscle cells (SMC) secrete insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) and an IGFBP-4 protease. The purpose of this study was to determine the characteristics of this IGFBP-4 protease and to compare its inhibitor profile to those of IGFBP-5 and IGFBP-2 proteases, which are also present in SMC-conditioned medium. Cultured SMC were exposed to serum-free medium for periods of 24-72 h, and the amount of proteolytic activity in the conditioned medium was assessed by its capacity to degrade pure IGFBP-4. Minimal activity (e.g. < 20% of IGFBP-4 degraded in 24 h at 37 C) was present in conditioned medium unless IGF-I or IGF-II was added. This resulted in more than 60% of the intact IGFBP-4 being degraded in 14 h. The activity was a calcium-dependent serine protease and was inhibited by EDTA or 3,4-dicloroisocoumarin. Calcium, but not zinc, could restore proteolytic activity. Heparin alone inhibited IGFBP-4 proteolysis by more than 60%. When heparin cofactor-II and antithrombin-III (AT-III) were added alone, they each had an effect. The combination of heparin plus AT-III was no more active than heparin alone, but the combination of heparin cofactor-II and heparin resulted in near complete inhibition. Peptides that contained the active sites of AT-III or alpha 1-antichymotrypsin were potent inhibitors of the IGFBP-4 protease. The medium also contained proteolytic activities for IGFBP-2 and IGFBP-5. Comparison of the inhibitor profiles for the IGFBP-4 and IGFBP-5 proteolytic activities revealed major differences, but the IGFBP-2 proteolytic activity was very similar to that of the IGFBP-4 protease. IGFBP-4 zymography showed a band with a molecular mass estimate of 48 kilodaltons. In contrast, when IGFBP-2 was used as the substrate, a single band at 36 kilodaltons was visualized. These data taken together with the protease inhibitor results suggest that the IGFBP-2, IGFBP-4, and IGFBP-5 proteases are members of a similar family of calcium-dependent serine proteases, but they are distinct proteases. As IGFBP-4 is a potent inhibitor of IGF action, and the activity of this protease is regulated by IGF exposure, the protease represents a novel system for regulating the actions of IGF-I in this cell type.

Circulating insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs) and tissue mRNA levels of IGFBP-2 and IGFBP-4 in the ovine fetus

The IGF-binding proteins (IGFBPs) are a family of at least six structurally related proteins, which bind the IGFs and modulate their actions, including the regulation of pre- and postnatal growth. In this study we have examined the relationship between circulating and tissue mRNA levels of IGFBPs and related this to circulating IGFs in the fetal sheep over the gestational period when rapid growth and development occurs. Circulating IGFBP-2, as measured by Western ligand blot (WLB), increases between early and mid gestation, remains high, then declines throughout late gestation (P = 0.0002). Circulating IGFBP-3 increases throughout gestation, as measured by WLB or RIA (P = 0.04 and P = 0.0001 respectively), as does circulating IGFBP-4 (P = 0.004). These ontogenic changes in circulating IGFBPs-2 and -4 are paralleled by changes in liver mRNA for these proteins and, for IGFBP-2, by those in kidney IGFBP-2 mRNA also. This suggests that liver and kidney may be the primary contributors to circulating IGFBP-2 and the liver to circulating IGFBP-4, IGFBP-2 mRNA is present in the heart and lung in early gestation but barely detectable in these tissues after approximately 60 days gestation. IGFBP-4 mRNA is also present in the heart in early but not late gestation, but is abundant in the lung throughout gestation. These results demonstrate tissue specific and developmental regulation of IGFBPs-2 and -4 at the mRNA level. To assess any role the circulating IGFs may play in mediating these changes in IGFBPs, or vice versa, both plasma IGF-I and IGF-II were measured by RIA. Circulating IGF-I increases as gestation progresses (P = 0.0001), while circulating IGF-II increases between early and mid gestation, remains high (P = 0.01), then declines. Circulating IGF-I is positively correlated with fetal weight (r = 0.66, P = 0.03), circulating IGFBP-3 (r = 0.54, P = 0.01) and IGFBP-4 (r = 0.52, P = 0.01). Circulating IGF-II positively correlates with circulating IGFBP-2 (r = 0.48, P = 0.02) throughout gestation and at 1 day postnatally. These relationships are consistent with circulating IGF-I influencing IGFBPs-3 and -4, and similarly, IGF-II determining IGFBP-2, or vice versa. Alternatively, these correlations may reflect coordinate regulation of IGF and IGFBP by a common factor.

Localization of cleavage site to non-homologous region of native IGFBP-4

Insulin-like growth factor binding protein 4 (IGFBP-4) is a 24-kDa protein that binds insulin-like growth factor 1 (IGF-1) and IGF-2 with high affinity and inhibits IGF action in vitro. We recently described a protease produced by the B104 neuronal cell line that cleaves IGFBP-4, yielding an approximate 16-kDa immunoreactive protein that binds IGFs with reduced affinity. We analyzed fragments produced by exposing pure IGFBP-4 to the protease to determine potential cleavage sites. Electrospray mass spectrometry and amino acid sequencing indicated the 16-kDa fragment spanned the NH2 terminus of native IGFBP-4 through Lys-120. There was evidence for an additional proteolytic fragment beginning at amino acid 132 and continuing to the COOH terminus. Proteolysis could be blocked by a synthetic peptide that spanned amino acids 117-126 but not by peptides that contained flanking sequences 111-120 or 125-135. Mutagenesis was used to alter the basic residue at position 120. The expressed mutant IGFBP-4 (K120A) was relatively resistant to cleavage, strongly suggesting that residues 120-121 represent the cleavage site. This region of IGFBP-4 is not homologous with other IGFBPs, explaining the apparent specificity of the protease for IGFBP-4. The 16-kDa IGFBP-4 fragment no longer inhibited IGF-1-stimulated thymidine uptake in vitro, suggesting that proteolytic processing of IGFBP-4 may have important functional consequences in vivo.

Expression of insulin-like growth factor binding proteins in the rat kidney: effects of long-term diabetes

Recent studies have shown that the renal synthesis of insulin-like growth factor binding proteins (IGFBPs) is altered in insulin-deficient diabetes mellitus, suggesting that these changes may be implicated in the alterations in renal function and morphology that accompany diabetes. To investigate the time course and the precise cellular distribution of changes in IGFBP expression, we used quantitative in situ hybridization to analyze renal IGF-I and IGFBP-1 to -5 messenger RNA (mRNA) localization and levels from 2 days to 6 months after the onset of streptozotocin-induced diabetes. There was an immediate sharp decline in IGF-I mRNA levels in the outer medulla that persisted for up to 3 months and a much smaller reduction in IGF-I mRNA levels in the medullary thick ascending limbs (MTALs). In nondiabetic animals, IGFBP-1 mRNA is most abundant in the MTALs. Immediately after the induction of diabetes, however, there was a greater than 2-fold increase in cortical IGFBP-1 mRNA and a 75% decrease in IGFBP-1 mRNA in MTALs. These changes persisted for up to 6 months in the diabetic animals. In contrast, IGFBP-5 mRNA levels were increased in the outer medulla and decreased in the cortex of diabetic kidneys. No significant changes in renal IG-FBP-2 mRNA levels or distribution were noted, and changes in IG-FBP-3 and -4 mRNA levels were subtle. In summary, streptozotocin-induced diabetes is associated with very prominent and complex alterations in renal IGF system gene expression, including robust increases in cortical IGFBP-1 and profound decreases in cortical IG-FBP-5 mRNA and medullary IGF-I mRNA levels. The divergent changes in IGFBP-1 and -5 mRNA levels in cortex vs. outer medulla indicate that regulation of IGFBP mRNA levels is quite complex.

Alterations in insulin-like growth factor (IGF)-dependent IGF-binding protein-4 proteolysis in transformed osteoblastic cells

Insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) is secreted by a variety of osteoblastic cells and appears to be an integral component of bone cell physiology. We have previously reported that normal human osteoblast-like (hOB) cells secrete IGFBP-4 as well as a novel IGFBP-4 protease, which requires IGF for functional activity. In this study we assessed the IGFBP-4/IGFBP-4 protease system in transformed osteoblastic cells by Western ligand blotting and cell-free IGFBP-4 protease assays. Simian virus-40-immortalized hOB cells (HOBIT), human osteosarcoma cells (TE-85), and rat osteosarcoma cells (UMR 106-01, ROS 17/2.8) secrete IGFBP-4. In contrast to the rapid and dramatic proteolysis in hOB medium, medium conditioned by these cells had no apparent IGFBP-4 protease activity when assayed with exogenous IGF-II in culture or under cell-free conditions. Assayed in the presence of exogenous protease. HOBIT cells, but not the osteosarcoma cell lines, appeared to produce a cycloheximide-sensitive inhibitor of the IGFBP-4 proteolytic reaction. Transient cell transformation induced by incubating human osteoblasts transfected with a temperature-sensitive mutant of simian virus-40 T-antigen at the permissive temperature or by treating hOB cells with phorbol ester tumor promoters also resulted in inhibition of IGF-dependent IGFBP-4 proteolysis. Inhibition was observed if phorbol ester was added to the cultures at the time of medium change or after the protease had been expressed and secreted. Differences in IGFBP-4 proteolysis could not be accounted for by changes in IGFBP-4 messenger RNA expression or substrate levels. These data suggest that transformation is associated with alterations in the IGFBP-4/IGFBP-4 protease system in osteoblastic cells. Normal human osteoblasts secrete an IGF-dependent IGFBP-4 protease. The induction of an inhibitor of the IGF-dependent IGFBP-4 proteolytic reaction may be associated with early transformation processes. Fully tumorigenic bone cells expressed neither IGFBP-4 protease nor protease inhibitor activity.

Effect of glucocorticoid on insulin-like growth factor (IGF) regulation of IGF-binding protein expression in fibroblasts

Insulin-like growth factor (IGF)-binding proteins (IGFBPs) can determine IGF biological competence at the cellular level. IGF-I itself has been shown to be an important peptide regulator of local IGFBP availability. Glucocorticoid also has major effects on IGFBP expression. In the present study, we assessed integrated IGF-I and glucocorticoid regulation of IGFBP messenger RNA (mRNA) and protein expression in two fibroblast model systems. In bovine fibroblasts, IGF-I treatment induced IGFBP-3 and IGFBP-5 mRNA and protein secretion, and had a moderate effect on IGFBP-4 expression. Dexamethasone had little effect on the IGF-induced increase in IGFBP-3, but completely blocked the increase in IGFBP-5 expression. Basal IGFBP-4 expression was inhibited by dexamethasone, and this effect was counteracted by IGF-I. IGFBP-2 expression did not vary with IGF-I or dexamethasone treatment in these cells; IGFBP-1 mRNA was not detectable, and IGFBP-6 mRNA was low and inconsistent. In human fibroblasts, IGF-I treatment increased levels of IGFBP-3 and decreased levels of IGFBP-4 without influencing mRNA expression. IGF-I also increased steady state levels of IGFBP-5 mRNA. Dexamethasone alone decreased IGFBP-3, IGFBP-4, and IGFBP-5 mRNA, but it had no significant effect on IGFBP-3, -4, or -5 expression in the presence of IGF-I. Human fibroblast IGFBP-6 expression was stable under the different culture conditions; IGFBP-1 and -2 mRNA were not detected. These data demonstrate that IGF peptide and glucocorticoid individually modulate IGFBP expression and indicate that glucocorticoid has distinct effects on IGF regulation of IGFBP depending upon the particular IGFBP and the underlying mechanism of IGF regulation. Bovine fibroblasts may provide a useful model system to probe the molecular mechanisms of IGFBP-3, -4, and -5 gene expression and regulation by IGF-I and glucocorticoid, whereas human fibroblasts may be suitable for studying posttranscriptional interactions.

Insulin-like growth factor I (IGF-I) and IGF binding proteins in seminal plasma before and after vasectomy in normal men

OBJECTIVE

To examine the levels and origins of insulin-like growth factor I (IGF-I) and insulin-like growth factor binding proteins (IGFBPs) in the human male genital tract.

DESIGN

Examining seminal plasma before and 3 months after vasectomy.

SUBJECTS

Fifteen men who were candidates for vasectomy were included in the study.

MAIN OUTCOME MEASURES

Seminal plasma and serum levels of IGF-I, IGFBP-1, and IGFBP-3 were determined by commercially available assays, furthermore, samples were subjected to Western ligand blotting.

RESULTS

Seminal plasma concentrations of IGF-I were significantly lower after vasectomy: 18.0 +/- 2.4 micrograms/L (before) and 12.5 +/- 1.2 micrograms/L (after). When the total ejaculate content of IGF-I was calculated, the figures were reduced by 50% after vasectomy: 45.64 +/- 7.8 ng (before) and 23.45 +/- 3.8 ng (after). The patterns observed for seminal plasma IGFBP-3 concentrations were 844.9 +/- 59 micrograms/L (before) and 816.5 +/- 65 micrograms/L (after). When the total ejaculate IGFBP-3 content was calculated there was a 36% reduction after vasectomy: 2,300 +/- 251 ng (before) and 1,474 +/- 217 ng (after).

CONCLUSIONS

A considerable amount of seminal plasma IGF-I and IGFBP-3 may be of testicular origin. Although the physiological significance of IGF-I and IGFBPs in the male reproductive system still remains uncertain, the demonstration of their presence in the testes add support to a functional role in the regulation of gonadal function.

Proteins in tissue extracts which bind insulin-like growth factor binding protein-3 (IGFBP-3)

Membrane associated IGFBP-3 is now known to play a role in the modulation of IGF at the cellular level, but mechanisms involved in cell membrane binding are far from certain. In this study we report the identification and initial structural characterisation of proteins in a range of sheep and rat tissues which specifically bind recombinant human non-glycosylated IGFBP-3. Tissues were homogenised in Tris HCl (0.1 M, pH 7.4), containing proteolytic enzyme inhibitors and the residues re-extracted in buffer containing SDS and Triton X-100 (both 1% w/v) prior to analysis. These were subjected to SDS-PAGE, electro-blotted onto nitrocellulose and subjected to ligand blot analysis (LBA) using radioiodinated IGFBP-3 as ligand. LBA revealed a major band of binding activity migrating at 60 kDa in extracts of rat muscle while sheep muscle contained forms of 52 and 40 kDa as the principal species and ovine pancreatic extracts an abundance of the 40 kDa variant alone. Distribution of the binding activity appears tissue specific. Apart from skeletal muscle, pancreas and a small amount of the 52 kDa form in pituitary, analysis revealed no evidence of IGFBP-3 binding in a range of other sheep tissues including liver, kidney, spleen, intestine, adrenal, brain, mammary, uterus, ovary and plasma. The binding activity is TCA precipitable, trypsin digestible, dose responsive and relatively specific for IGFBP-3 since the related proteins recombinant human IGFBP-2 and purified caprine IGFBP-4 failed to bind.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor-I improves mucosal structure and function in transplanted rat small intestine

The transplanted small intestine develops significant mucosal atrophy, impaired nutrient and water absorption, and increased bacterial translocation to mesenteric lymph nodes in rats maintained on elemental diets or total parenteral nutrition. This study determined the effects of administration of an peptide growth factor (insulin-like growth factor-I[IGF-I]) on the mucosal structure and barrier function of rat small bowel isografts. Thirty-six adult Lewis rats underwent either resection of the distal 60% of the small bowel and proximal colon followed by a 40-cm orthotopic jejunal isograft or proximal small bowel transection and distal small bowel resection to leave an analogous length of small intestine in control animals. All rats received an isocaloric, isonitrogenous, polymeric diet (200 kcal/kg/day, 2 gN/kg/day) by gastrostomy and were infused with either IGF-I (2.4 mg/kg/day) or vehicle by osmotic pumps subcutaneously. After 10 days of treatment, jejunal crypt cell production, mucosal morphometric indices, glucose and water absorption, body weight, and bacterial translocation to mesenteric lymph nodes (MLN) were measured. Jejunal mRNA content for IGF-I, IGF-I receptor, and IGF-binding proteins 3 and 4 (IGFBP-3,4) were determined by Northern blotting. Crypt cell production, villus height, crypt depth, and villus surface area were significantly increased in control and transplanted jejunum of rats infused with IGF-I when compared to animals given vehicle alone. Additionally, jejunal glucose absorption and water absorption were significantly improved in both IGF-I groups when compared with their respective vehicle controls. IGF-I infusion increased body weight in transplanted and control animals and markedly reduced bacterial translocation to MLN after small bowel transplantation. Jejunal levels of IGF-I mRNA were significantly increased in transplanted animals when compared to transected controls. IGF-I treatment significantly increased IGFBP-3 tissue mRNA levels in both transected and transplanted animals. These results demonstrate that IGF-I administration, after small bowel transplantation, improves mucosal structure and absorptive function and reduces bacterial translocation to MLN. IGF-I may have important effects in transplanted small bowel both as an endogenous and administered growth factor.

Cleavage analysis of insulin-like growth factor (IGF)-dependent IGF-binding protein-4 proteolysis and expression of protease-resistant IGF-binding protein-4 mutants

Cultured human fibroblasts and osteoblast-like cells secrete an insulin-like growth factor (IGF)-dependent protease that cleaves IGF-binding protein-4 (IGFBP-4) into two fragments of approximately 18 and 14 kDa. Edman degradation of the isolated proteins established the amino termini of the reaction products. Sequence analysis of the 14-kDa carboxyl-terminal half of IGFBP-4 suggested cleavage after methionine at position 135 of the mature protein. Four variant IGFBP-4 molecules with single amino acid substitutions around this cleavage site were constructed and expressed. Wild-type and mutant IG-FBPs-4 bound IGF-I and IGF-II with equivalent affinities and, in the intact state, were equally effective inhibitors of IGF-I action. However, the IGFBP-4 mutants were relatively resistant to IGF-dependent proteolysis. A 5-6-h incubation in human fibroblast conditioned medium in the presence of IGF-II was sufficient for near total hydrolysis of wild-type IGFBP-4, whereas the mutant IGFBPs-4 were only minimally affected at this time. After a 24-h incubation with IGF-II, all mutant IGFBPs-4 showed extensive proteolysis, generating 18- and 14-kDa fragments. Pre-exposure of human fibroblasts in serum-free conditioned medium to IGF-II for 5 h potentiated subsequent IGF-I stimulation of DNA synthesis. When added with IGF-II, the protease-resistant mutant IG-FBPs-4, but not wild-type IGFBP-4, suppressed IGF-II enhancement of IGF-I-stimulated DNA synthesis. These biological studies suggest that the IGFBP-4/IGFBP-4 protease system may play a role modulating local cellular response to IGF-I.

IGF binding proteins-4, -5 and -6 may play specialized roles during L6 myoblast proliferation and differentiation

It is well known that IGFs-I and -II stimulate both the proliferation and differentiation of myoblasts, but the role of the IGF binding proteins (IGFBPs) during these processes has not been established. In this study we show that IGF-I analogs with greatly reduced affinity for IGFBPs exhibited about a 10-fold increase in potency in stimulating proliferation (as in other cell types), but up to a 100-fold greater potency than native IGF-I in stimulating L6A1c differentiation. Analysis of conditioned media revealed that L6 cells secrete significant levels of IGFBPs that react with antisera to IGFBP-4, -5 and -6. Steady-state levels of IGFBP-4 mRNA were highest in proliferating myoblasts, while IGFBP-5 mRNA could not be detected in myoblasts although its levels were dramatically increased during IGF- or insulin-stimulated differentiation of myoblasts into myotubes. Elevated IGFBP-6 mRNA levels were found in quiescent cells in serum-free medium. IGF-I and IGF-II treatment elevated IGFBP-5 in conditioned media, but longR3IGF-I and insulin, which do not bind to IGFBPs, had smaller effects. This complex regulation of expression of different IGFBPs not only during different stages of muscle growth and differentiation, but also upon stimulation by IGFs or insulin, suggests that the IGFBPs play a specific and significant role in modulating the actions of the IGFs during myogenesis.

Development of smooth muscle hypertrophy is closely associated with increased gene expression of insulin-like growth factor binding protein-2 and -4

The aim of the present investigation was to study the role of the IGF system in the development of smooth muscle hypertrophy. Hypertrophy was initiated by partial ligation of the urethra in female Sprague-Dawley rats. The solution hybridization assay was used to analyse the mRNA levels. Ligation of the urethra induced a sustained increase in bladder wet weight during the following 6-week period studied. IGF-I mRNA increased from 1 to 3 amol/micrograms DNA 1-day after ligation, peaked at 3-days (4-fold), and normalized 6-weeks after ligation. In hypertrophying bladder, IGFBP-2 and -4 mRNA increased sharply during the first 10 days (5-fold) and remained elevated during the 6-week period. The IGF-I receptor mRNA did not change significantly. Removal of the obstruction 10 days after ligation caused a regression of bladder wet weight, and resulted in normalization of IGF-I, IGFBP-2 and -4 mRNA. The results show a close correlation between progression or regression of smooth muscle hypertrophy and differential regulation of IGF-I, IGFBP-2 and -4 mRNA, indicating that the IGF system may play a role in smooth muscle hypertrophy.

Regulation of insulin-like growth factor-binding protein-4 in human endometrial stromal cell cultures: evidence for ligand-induced proteolysis

The present study investigates the regulation of IGFBP-4 levels by insulin-like growth factor (IGF) peptides in human endometrial stromal cell cultures. A 24-kilodalton (kDa) IGF-binding protein (IGFBP) secreted by stromal cells was identified as IGFBP-4 by immunoprecipitation and Western ligand blotting. Western ligand blot analysis of conditioned medium showed that treatment of stromal cells with IGF-I or IGF-II induced a dose-dependent reduction of detectable IGFBP-4 levels. Two IGF analogs that bind type I IGF receptors, but have reduced affinity for IGFBPs, increased detectable levels of IGFBP-4, and their ability to reduce IGFBP-4 at high concentrations was positively correlated with their affinity for this binding protein. LR3-IGF-I, which has 1000-fold lower binding affinity than IGF-I, increased detectable IGFBP-4 at all concentrations tested. Des-(1-3)-IGF-I, whose affinity for IGFBP-4 is 30-fold lower than that of IGF-I, increased detectable IGFBP-4 at low concentrations (0.1-10 ng/mL), but reduced its levels at 100 ng/mL, consistent with the significant binding to IGFBP-4 at this concentration. In contrast, IGFBP-4 was undetectable in cultures receiving Leu27-IGF-II, which has reduced affinity for the type IIGF receptor but unaltered affinity for IGFBPs and the type II receptor. High concentrations of insulin (100 ng/mL), which interacts with type I IGF receptors without binding IGFBPs, also increased detectable levels of IGFBP-4 in stromal cultures. The addition of IGF-I or IGF-II to cell-free conditioned medium from stromal cells cultured in the absence of IGFs resulted in the reduction of detectable endogenous IGFBP-4 levels. The effects of IGFs on IGFBP-4 levels in this cell-free system were time, temperature, and pH dependent and were prevented by the serine proteinase inhibitor, aprotinin, by the divalent cation chelator, EDTA, and by the metal ion chelator, 1,10-phenanthroline. Western immunoblotting showed that the IGF-induced reduction of intact 24-kDa IGFBP-4 was accompanied by the generation of an immunoreactive fragment of approximately 16 kDa, which was not detectable by Western ligand blotting. Cell-free conditioned medium from endometrial stromal cultures proteolyzed covalently cross-linked [125I]IGF-II-IGFBP-4 complexes in the absence of added IGFs, generating an 18-kDa radiolabeled fragment, and addition of free IGF peptide did not enhance the degradation of IGF-II-IGFBP-4 complexes.(ABSTRACT TRUNCATED AT 400 WORDS)

IGF-binding proteins in human prostate tumor cells: expression and regulation by 1,25-dihydroxyvitamin D3

The expression of the six known insulin-like growth factor binding proteins (IGFBPs) and their corresponding messenger RNAs has been examined in three cell lines established from surgical and biopsy specimens of human prostate carcinoma. All three cell lines produced both IGFBP-4 and IGFBP-6 and the respective mRNAs; expression of IGFBP-6 has not been previously demonstrated in human prostate tumor cells. No other binding proteins were detected. The levels of IGFBP mRNAs were not regulated by androgens or IGF-1, but the level of IGFBP-6 mRNA was sharply increased by 1,25-dihydroxyvitamin D3 (1,25(OH)D3). The stimulation was dose-dependent with a maximum effect at 10 nM 1,25(OH)D3 and a clearly discernible effect at 0.1 nM. The results support a role for vitamin D in the control of prostate tumor growth, mediated at least in part by interaction with IGFs and specific IGFBPs.

Plasma growth hormone-binding protein activity, insulin-like growth factor I, and its binding protein levels in patients with Turner's syndrome: effect of short- and long-term recombinant human growth hormone administration

Plasma growth hormone-binding protein (GH-BP) activity and the levels of IGF-I and its binding proteins (IGFBP) were studied in eight girls with Turner's syndrome before and during recombinant-hGH (r-hGH) administration. Growth hormone and GH-BP activity were assayed at baseline and hourly, over a 12-h period, after an intramuscular bolus of 0.09 mg/kg of the hormone. After 7 d, each patient received r-hGH at 0.33 mg/kg/weekly s.c. every day at nighttime; plasma growth hormone-binding protein activity, blood IGF-I, and IGFBP were evaluated before and on d 7, 30, 180, and 360. Baseline reference values were obtained from 10 bone age-matched healthy girls. Basal GH-BP activity, IGF-I, and IGFBP levels were similar in patients and controls. Four h after the intramuscular injection, GH-BP activity maximally increased and returned to baseline 6-7 h later; during long-term r-hGH administration GH-BP activity peaked at +180 d but declined to pretreatment at +360 d. IGF-I, IGFBP-3, and IGFBP-4 increased under r-hGH and, in contrast to GH-BP activity, remained high throughout the study. In conclusion, in girls with Turner's syndrome, GH-BP activity, IGF-I, IGFBP-3, and IGFBP-4 are induced by r-hGH. However, the increase of IGF-I and IGFBP-3 does not require an increased level of the cellular growth hormone receptors, as suggested by the unchanged +360 d values of plasma GH-BP activity compared with baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Episomal expression of sense and antisense insulin-like growth factor (IGF)-binding protein-4 complementary DNA alters the mitogenic response of a human colon cancer cell line (HT-29) by mechanisms that are independent of and dependent upon IGF-I

HT-29 cells express and secrete insulin-like growth factor (IGF)-II and only one of the six IGF-binding proteins, IGFBP-4. In the present study, the physiological role of endogenous IGFBP-4 in regulating the growth response of HT-29 cells to exogenous and endogenous IGFs was examined. Both the basal and the IGF-stimulated growth of HT-29 cells was significantly increased over control values in the presence of IGFBP-4 antibody, suggesting that endogenous IGFBP-4 is a potent inhibitor of the mitogenic effects of endogenous and exogenous IGFs. In order to further confirm the inhibitory role of endogenous IGFBP-4, sense and antisense complementary DNA fragments of human IGFBP-4 were ligated into an episomal mammalian expression vector (pCEP4). Restriction mapping and Southern blot analysis were used to confirm directional cloning of the IGFBP-4 complementary DNA fragments in the sense and antisense directions in the pCEP4 vectors. HT-29 cells were transfected with either the control (no insert, C-P), sense (S-P), or antisense (AS-P) vectors and subjected to hygromycin selection. The functional nature of the transfectants was confirmed by measuring IGFBP-4 concentrations in the conditioned media (CM) of 10(7) cells by ligand and immunoblot analysis. IGFBP-4 concentrations were 7.4 +/- 1.7-fold higher in the CM of S-P cells compared to that in the CM of C-P cells, while IGFBP-4 concentrations in the CM of AS-P cells were significantly lower than those present in the CM of C-P cells. Both the basal and the IGF-I-stimulated growth of the AS-P cells was significantly higher than that of the C-P and S-P cells. The basal (non-stimulated) and the IGF-I-stimulated growth of the S-P cells was not significantly different from that of the C-P cells, suggesting that overexpression of IGFBP-4 was not inhibitory to the growth of the HT-29 cells. The basal growth of the S-P and C-P cells was significantly increased in the presence of IGFBP-4 antibody, once again suggesting that endogenous IGFBP-4 was a potent inhibitor of autocrine effects of endogenous factors (IGF-II). Addition of IGFBP-4 antibody had no significant effect on the basal growth of the AS-P cells, confirming that the difference between the growth response of the AS-P, C-P, and S-P cells was largely contributed by the difference in the endogenous secretion of IGFBP-4 by the cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of insulin-like growth factor-binding proteins produced by cultured fibroblasts from patients with noninsulin-dependent diabetes mellitus, insulin-dependent diabetes mellitus, or obesity

To evaluate whether the production of insulin-like growth factor-binding proteins (IGFBPs) is altered in various pathological states due to modification of the hormonal milieu, we analyzed patterns of IGFBPs released into conditioned medium during 48-h serum-free culture of early passages of human skin fibroblasts from control subjects and patients with metabolic disorders. IGFBP-2, -3, -4, and -5 were identified in the conditioned medium by immunoblotting or RIA. Compared with those in eight control subjects by ligand blot analysis, the levels of IGFBP-3, -2, and -5 were reduced to 43%, 47%, and 53% in 10 noninsulin-dependent diabetic patients, respectively, whereas the levels of IGFBP-3 and -2 were reduced to 36% and 23%, respectively, in 3 nondiabetic obese patients with impaired glucose tolerance. In 2 insulin-dependent diabetic patients, the level of IGFBP-3 was reduced by 25% and 40%, respectively, and IGFBP-2 was not detectable. In contrast, a similar level of IGFBP-4 was detected in both normal and patient's conditioned media, except in 1 insulin-dependent diabetic patient. These data indicate that fibroblasts derived from patients with metabolic disorders retain their intrinsic characteristics even after they are removed from their in vivo hormonal milieu.

The insulin-like growth factor-binding protein-4 (IGFBP-4)-IGFBP-4 protease system in normal human osteoblast-like cells: regulation by transforming growth factor-beta

Insulin-like growth factor-binding protein-4 (IGFBP-4) is secreted by normal human osteoblast-like (hOB) cells and acts as a potent inhibitor of IGF action. hOB cells also secrete a protease, which requires IGFs for activation and specifically cleaves IGFBP-4. To study the regulation of this IGFBP-4 protease, hOB cells from 26 different adult donors were cultured in serum-free medium for 24 h in the absence or presence of hormones and other factors known to regulate bone growth. hOB cell-conditioned medium (hOB-CM) was collected for measurement of IGFBP-4 protease activity in a cell-free assay. This assay involved incubation of hOB-CM (50 microL) without or with IGF-II at 37 C for 6 h. IGF-II-activated IGFBP-4 hydrolysis was assessed by Western ligand blotting and quantitated using laser densitometry. Conditioned medium from all hOB cells examined exhibited IGFBP-4 protease activity. PTH, GH, insulin, calcitonin, glucocorticoids, sex steroids, 1,25-dihydroxyvitamin D3, and epidermal growth factor had no significant effect on IGF-dependent IGFBP-4 protease activity. In comparison, hOB-CM from cells treated with transforming growth factor-beta (TGF beta) exhibited significantly augmented IGF-II-dependent proteolysis of endogenous IGFBP-4. Enhanced proteolysis of exogenous IGFBP-4 was also demonstrated: 1) 92% of recombinant human IGFBP-4 added to conditioned medium from TGF beta-treated hOB cells was hydrolyzed during the assay in the presence of IGF-II compared to 45% of recombinant human IGFBP-4 added to control hOB-CM; and 2) increased radiolabeled IGFBP-4 fragments were generated in conditioned medium from TGF beta-treated hOB cells compared with control hOB-CM in the presence of IGF-II. In addition to its effect on IGFBP-4 proteolysis, TGF beta treatment decreased IGFBP-4 messenger ribonucleic acid expression, as measured by Northern analysis. Our results indicate that the IGFBP-4-IGFBP-4 protease system in hOB cells can be controlled by two of the most abundant local growth factors for bone (IGF-II and TGF beta), with each acting via different mechanisms. Regulation of IGFBP-4 availability may play an important role in the modulation of bone cell responsiveness to IGFs.

Insulin-like growth factor system gene expression in human endometrium during the menstrual cycle

To study the cellular patterns of gene expression of the insulin-like growth factor (IGF) system in human endometrium during the menstrual cycle, we used in situ hybridization histochemistry to localize messenger ribonucleic acids (mRNAs) encoding IGF-I and -II, their receptors, and their binding proteins (IGFBPs) in fresh-frozen endometrial tissue obtained from cycling women. IGF-I and IGF-II mRNAs are both expressed diffusely throughout endometrial stroma and are not detected in endometrial epithelium. Endometrial IGF-I mRNA is significantly more abundant during the proliferative than the secretory phase of the menstrual cycle, whereas the reverse is true for IGF-II. Type I and type II IGF receptor mRNAs are both present in endometrial stroma, but are relatively more abundant in endometrial epithelium, and neither shows distinctive cyclic changes. IGFBP-2, -4, -5, and -6 mRNAs demonstrate a diffuse stromal pattern of expression, whereas IGFBP-1 and -3 are more focally concentrated in selected subpopulations of endometrial cells. IGFBP-1 mRNA is not detected in proliferative endometrium and demonstrates a very heterogeneous pattern of expression in secretory endometrium, where it is intensely abundant in a patchy distribution of stromal and epithelial cells. IGFBP-3 mRNA is primarily concentrated in endometrial capillaries and is increased in the secretory phase, largely due to the intense vascularization of endometrial glands during this phase. IGFBP-5 mRNA is more abundant in the proliferative phase, but all other IGFBP mRNAs are relatively increased in the secretory phase of the menstrual cycle. These findings support the view that the IGF system plays a fundamental role in endometrial biology, acting via autocrine and/or paracrine mechanisms, with IGF-I and IGFBP-5 being dominant in the proliferative phase, and IGF-II and the other IGFBPs predominant in the secretory phase of the menstrual cycle.

IGF-binding proteins are differentially regulated in an ovarian granulosa cell line

We have recently established an immortalized granulosa cell line as a model system to investigate ovarian function, with particular emphasis on the insulin-like growth factor (IGF) regulatory system. Previous results have shown that these cells express mRNAs for IGF-binding proteins (IGFBPs)-2 to -5. These IGFBPs are also detected by ligand blots. The current work evaluated the regulation by the IGFs and cAMP on the IGFBPs and their mRNAs and compared the findings to that in primary culture. Our results indicate that levels of the IGFBPs are controlled, in part, by expression of the mRNAs. However, evidence for post-transcriptional regulation was also discovered. IGFBP-3 was stimulated by IGF-I, IGFBP-4 by forskolin, and IGFBP-5 by IGF-I. IGFBP-2, -3, and -4 are expressed under basal conditions whereas IGFBP-5 is only detectable after IGF-I induction. An alteration in the biphasic actions of cAMP in this cell line, as compared to primary culture, was evident.

Hypertension increases insulin-like growth factor binding protein-4 mRNA levels in rat aorta

Insulin-like growth factor-I (IGF-I) is an endocrine and autocrine/paracrine growth factor. Recently, we have demonstrated that interrenal aortic coarctation in the rat increases IGF-I mRNA levels in the thoracic aorta, consistent with a role for this mitogen in hypertensive vascular remodeling. The effects of IGF-I are modulated by several IGF binding proteins including IGFBP-3, the main circulating carrier of IGF-I, and IGFBP-4, the main IGF binding protein produced by vascular smooth muscle cells in vitro. To obtain insights into the regulation of IGF-I and more specifically to study potential changes in IGF binding proteins in high-renin hypertension, we studied male Sprague-Dawley rats that had undergone abdominal aortic coarctation. Compared with sham-operated rats, the study rats showed a rapid increase in IGFBP-4 mRNA levels in the hypertensive (thoracic) aorta, reaching a plateau at 3 days (2.5-fold increase) and persisting for at least 14 days. In striking contrast, IGFBP-4 mRNA decreased slightly in the normotensive (abdominal) aorta at 14 days. IGFBP-3 mRNA levels did not change in either vascular bed after coarctation. Study of hepatic tissue indicated that in coarcted rats IGFBP-4 and IGFBP-3 mRNA levels decreased transiently (approximately 50% at 7 days compared with sham). Circulating IGF-I in coarcted animals decreased slightly (P = .08), and Western ligand analysis indicated that circulating levels of IGF binding proteins were not altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of messenger ribonucleic acid for insulin-like growth factor-binding proteins in human skin by in situ hybridization

The role of the insulin-like growth factors (IGFs) in human skin physiology has been increasingly recognized, although relatively little is known about the cell types involved or the cellular mechanisms that mediate these responses. Epidermal keratinocytes and dermal fibroblasts both possess IGF-I receptors and are responsive to IGF-I. IGF-binding proteins (IGFBPs), known modulators of IGF action, may also be responsible for targeting IGF-I to its receptors and are produced by both cultured keratinocytes and fibroblasts. To demonstrate sites of production of IGFBPs in human skin, we have used in situ hybridization to localize messenger ribonucleic acid (mRNA) for the six IGFBPs. Antisense and sense RNA probes for the IGFBPs (IGFBP-1 to -6) were produced, and 5-microns sections of normal adult human male chest skin were probed. The control probe used was keratin-5, which is known to hybridize to the basal keratinocytes of the epidermis. mRNAs for human IGFBP-2, -3, -4, and -5 were identified, with mRNAs for IGFBP-2 and IGFBP-4 localized in sebaceous glands and eccrine sweat glands (epidermal origin), IGFBP-3 mRNA in the basal layer of the epidermis and mRNAs for IGFBP-4, and IGFBP-5 found throughout the dermis. mRNAs for IGFBP-1 and -6 were not identified in human skin. These studies demonstrate specific localization of IGFBP mRNAs in adult human skin, suggesting that each IGFBP may play a specific role in targeting IGF-I to its receptor on responsive cells and, ultimately, in modulation of IGF-I action in skin.

Consequences of postnatally elevated insulin-like growth factor-II in transgenic mice: endocrine changes and effects on body and organ growth

Insulin-like growth factor-II (IGF-II) is an important regulator of embryonic growth and differentiation, but its function in postnatal life is unclear. To address this point, we generated transgenic mice harboring fusion genes in which a human IGF-II complementary DNA is placed under the transcriptional control of the rat phosphoenolpyruvate carboxykinase promoter. Transgene-specific messenger RNA was detected in liver, kidney, and several parts of the gut. Serum IGF-II levels in transgenic mice were 2-3 times higher than those in controls and increased after starvation. Circulating IGF-I correlated negatively and IGF-binding protein-2 (IGFBP-2) positively with IGF-II levels, suggesting that IGF-I is displaced from IGFBPs by IGF-II and that IGF-II is a major regulator of IGFBP-2. Serum levels of IGFBP-3 and IGFBP-4 tended to be higher in phosphoenolpyruvate carboxykinase-IGF-II transgenic mice than in controls, as evaluated by ligand blot analysis. Starvation reduced serum IGF-I, but increased IGFBP-2 in transgenic mice more markedly than in controls. Fasting insulin levels were significantly reduced in transgenic mice, whereas glucose levels were not influenced by elevated IGF-II. The body growth of 4- and 12-week-old mice was not significantly influenced by elevated IGF-II, but transgenic mice displayed increased kidney and testis weight at the age of 4 weeks, and increased adrenal weight at the age of 12 weeks. Our results demonstrate that elevated IGF-II in postnatal life has multiple endocrine consequences and subtle time-specific effects on organ growth.

Identification of insulin-like growth factor-binding protein-3 (IGFBP-3) fragments and IGFBP-5 proteolytic activity in human seminal plasma: a comparison of normal and vasectomized patients

Previous studies have demonstrated that insulin-like growth factor (IGF) peptides, IGF-binding proteins (IGFBPs), and IGFBP-3 proteolytic activity, are present in human seminal plasma (SP). In this study, we have further characterized the IGFBPs in SP using immunoprecipitation and Western ligand blotting, Western immunoblotting, affinity cross-linking and immunoprecipitation, and RIA of IGFBP-3 using two different assays and have identified additional proteolytic activities for IGFBP-4 and IGFBP-5 in SP. Immunoprecipitation with antibodies to IGFBP-2, IGFBP-3, and IGFBP-4, before and after affinity cross-linking, demonstrated that intact IGFBP-2 and IGFBP-4 are present in SP, but intact IGFBP-3 is absent. Low mol wt fragments of IGFBP-3, which did not bind to IGF-I or IGF-II on Western ligand blot and did not cross-link to IGF-II, were demonstrated on Western immunoblot and were measurable by two different RIAs. Proteolytic activities for IGFBP-4 and IGFBP-5 were demonstrated in SP by incubation with the respective iodinated IGFBPs. On comparing the proteolytic activity for IGFBP-4 by purified prostate-specific antigen (PSA; a known IGFBP-3 protease in SP) or by SP with measured equivalent concentrations of PSA, the dose response and fragment patterns were identical. With IGFBP-5, however, proteolysis by purified PSA was different from that by SP with measured equivalent concentrations of PSA: 1) proteolysis by pure PSA was less efficient than matched concentrations of SP; 2) the pattern of fragments after proteolysis by pure PSA was different from that after proteolysis by matched concentrations of SP; and 3) proteolysis by purified PSA was significantly inhibited by phenylmethylsulfonylfluoride and aprotinin, but proteolysis by SP was not. We conclude that human SP contains intact IGFBP-2 and IGFBP-4, but has only IGFBP-3 fragments with low affinity for IGF peptides; that PSA is able to proteolyze IGFBP-4 and IGFBP-5 (as well as IGFBP-3); and that an additional IGFBP-5 protease is probably present in SP. There was no significant difference in any of these findings in SP from normal volunteers, vasectomized patients, or patients with idiopathic azoospermia. The roles of IGFBPs and IGFBP proteases in the male reproductive system and male infertility remain to be further elucidated.

Expression of insulin-like growth factor-I (IGF-I) and IGF-binding proteins during adipogenesis

Insulin-like growth factor-I (IGF-I) stimulates the differentiation of preadipocytes, but the expression of IGF-I and IGF-binding proteins (IGFBPs) during the course of adipogenesis has not been investigated. Using two in vitro models, primary mouse preadipocytes and the 3T3-L1 preadipocyte cell line stimulated to differentiate with IGF-I, we studied IGF and IGFBP expression before and during differentiation. Primary preadipocyte cultures expressed IGF-I, IGFBP-2, and IGFBP-4 messenger RNAs (mRNAs), and conditioned medium (CM) contained IGFBP-3 [approximately 46,000 mol wt (M(r))], IGFBP-4 (24,000 M(r)), and a 30,000 M(r) IGFBP identified by immunoblot as IGFBP-2. During differentiation, an additional approximately 34,000 M(r) form of IGFBP-2 was predominant, but IGFBP-2 mRNA decreased, suggesting that a mechanism other than steady state mRNA levels is regulating protein abundance in CM. Like primary cultures, undifferentiated 3T3-L1 cells expressed IGFBP-4 mRNA, but insignificant levels of IGF-I and IGFBP-2 mRNAs. 3T3-L1 cell CM contained IGFBP-3 and IGFBP-4, and with the addition of IGF-I, a 30,000 M(r) IGFBP was also present. This IGFBP was not recognized by antiserum to IGFBP-1, -2, -4, -5, or -6. During differentiation of 3T3-L1 cells, an approximately 34,000 M(r) form of IGFBP-2 was also present in CM. In summary, primary cultures of mouse preadipocytes and 3T3-L1 cells express similar IGFBPs during IGF-I-stimulated adipogenesis. The presence of a larger isoform of IGFBP-2 in a differentiation-dependent manner and a potentially novel IGFBP in response to IGF-I suggests that these IGFBPs may be important in modulating IGF-I action in adipogenesis.

Differential regulation of insulin-like growth factor binding protein-2 and -4 mRNA in muscle tissues and liver by diabetes or fasting

The present study was undertaken to investigate the metabolic regulation of insulin-like growth factor binding proteins (IGFBPs) gene expression in muscles from diabetic or fasted rat. The messenger RNA (mRNA) levels for IGFBP-2 and -4 were analysed by solution hybridization in heart, skeletal and smooth muscle and liver from fasted (3 days) and refed (6, 12, 24, 72 h) rats and rats made diabetic with streptozotocin. In aortic intima-media, the mRNA levels for IGFBP-2 and -4 were decreased by diabetes or fasting and were restored gradually by refeeding. The response of IGFBP-4 mRNA to diabetes appeared two days after injection of streptozotocin, while a significant decrease of IGFBP-2 mRNA was found after a diabetes duration of two weeks. Both diabetes and fasting decreased IGFBP-4 mRNA levels in heart muscle and skeletal muscle and refeeding restored mRNA for IGFBP-4 to normal level. IGFBP-2 mRNA was undetectable in heart muscle and skeletal muscle. In liver IGFBP-4 mRNA was abundantly expressed. It was slightly but significantly decreased by fasting and approached normality with refeeding, while no change was found in diabetic liver. In contrast, liver IGFBP-2 mRNA was much lower in amount than IGF-I mRNA and IGFBP-4 mRNA and was sharply elevated by fasting, and decreased by refeeding. In conclusion, 1) both IGFBP-2 and -4 mRNA in various tissues are regulated by diabetes or fasting; 2) the mRNA for IGFBP-2 is metabolically regulated in a discordant, organ-specific manner.

Insulin-like growth factor axis abnormalities in prostatic stromal cells from patients with benign prostatic hyperplasia

Benign prostatic hyperplasia (BPH) is a common proliferative disorder of unknown etiology. To assess whether patients with BPH have alterations in their prostatic IGF axis, we measured the expression (by Northern blotting) and the production (by Western ligand blotting and RIA) of insulin-like growth factor-II (IGF-II) and IGF-binding proteins (IGFBPs) in prostatic epithelial and stromal cell strains grown from normal (n = 7), hyperplastic (n = 7), and malignant (n = 5) surgical specimens. Levels of IGF-II messenger ribonucleic acid (mRNA; normalized for actin expression) were 10-fold higher in BPH stromal cell strains compared to those in normal stromal cell strains (P < 0.0001). Western ligand blotting of conditioned medium (CM) from normal stromal cells demonstrated the presence of IGFBP-2, -3, and -4. In the CM of BPH stromal cells, IGFBP-2 levels were dramatically reduced to less than 20% of normal (P < 0.001). Additionally, IGFBP-5, which was not observed in significant amounts in normal stromal cell-CM, was found in large quantities in BPH stromal cell-CM. Northern blot analysis of mRNA from normal and BPH stromal cells demonstrated a 5-fold decrease in IGFBP-2 mRNA (P < 0.001) and a 4-fold increase in IGFBP-5 mRNA (P < 0.01) in BPH compared to normal cells. In prostate stromal cells from cancer specimens, no abnormalities were found. No abnormalities were observed in the IGF axis parameters evaluated in prostate epithelial cells from BPH or cancer strains. We conclude that prostatic stromal cell strains isolated from patients with BPH hyperexpress the mRNA for IGF-II and IGFBP-5 while expressing reduced amounts of IGFBP-2 mRNA. IGFBP, but not IGF-II, peptide levels in CM correspond to the mRNA differences. This is the first documentation of altered gene and protein expression in this common disease. We speculate that these abnormalities in the IGF axis may be important in the pathogenesis of BPH.

Isolation and characterization of ovine IGFBP-4: protein purification and cDNA sequence

Three different molecular mass forms of IGF-binding proteins (IGFBPs) were purified from ovine plasma by IGF-I affinity chromatography and reverse-phase HPLC: a 46 kDa doublet and 29 kDa and 24 kDa forms. Amino-terminal sequence analysis confirmed that these proteins were ovine (o)IGFBP-3 (46 kDa) and two molecular size variants of oIGFBP-4. oIGFBP-3 and the 29 kDa form of oIGFBP-4 were shown to be N-glycosylated. Isoelectric points were determined to be at approximately pH 6 for oIGFBP-3 and at pH 7 and pH 7.5 for the 29 and 24 kDa forms of oIGFBP-4 respectively. The two different molecular mass variants of oIGFBP-4 had similar IGF-binding properties. Compared with human IGFBP-3 and oIGFBP-3, the two variants of oIGFBP-4 exhibited lower relative binding to amino-terminally modified IGF-I analogues in a competitive IGF-binding assay. The full protein sequence of oIGFBP-4, as deduced from the cDNA sequence, showed a high degree of identity with rat (90%), human (96%) and bovine (98%) IGFBP-4. The cDNA sequence also showed homology over regions of the 3' non-coding sequence, particularly in comparison with bovine IGFBP-4 (96%). Northern analysis of mRNA for oIGFBP-4 indicated a 2.6 kb major transcript and two minor transcripts of approximately 2.1 and 1.8 kb. oIGFBP-4 mRNA transcripts were detected in adult ewe liver > kidney > lung >> heart and also in several fetal tissues, thus suggesting tissue-specific and developmental regulation. The availability of purified oIGFBP-4 and oIGFBP-3 as well as DNA probes for oIGFBP-4 will enable further study of the properties and functions of these proteins, as well as the establishment of specific assays for these IGFBPs.

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.

Glucocorticoid regulation of an insulin-like growth factor-binding protein-4 protease produced by a rat neuronal cell line

Insulin-like growth factor-binding protein-4 (IGFBP-4) is expressed in distinct regions in the rodent brain from the perinatal period into adulthood and is postulated to modulate the action of the insulin-like growth factors (IGFs) in vivo. This study was initiated to examine the regulation of IGF-binding protein-4 (IGFBP-4) in B104 cells, a rat neuronal cell line in which IGFBP-4 is the predominant secreted IGFBP. Exposure of B104 monolayer cultures to dexamethasone reduced native IGFBP-4 abundance to less than 10% of that in control medium by 48 h. Immunoblots showed that the decline in intact 24-kilodalton IGFBP-4 was accompanied by an increase in a 16-kilodalton immunoreactive fragment. In addition, IGFBP-4 proteolytic activity in medium was increased after exposure of the cells to dexamethasone. The protease was calcium dependent and appeared to be of the serine protease class, because activity could be inhibited by phenylmethylsulfonylfluoride and aprotinin, but not antipain, leupeptin, or pepstatin. Although the proteolytically modified IGFBP-4 retained the ability to bind IGFs, the affinities were approximately 13- and 20-fold lower for IGF-I and IGF-II, respectively. These data indicate that B104 cells produce an IGFBP-4 protease that is regulated by glucocorticoids. The actions of this protease reduce the affinity of IGFBP-4 for the IGFs without abolishing binding. Because both the IGFs and glucocorticoids have important roles in brain development, it is possible that some glucocorticoid actions in the brain could be mediated by proteolysis of IGFBP-4, which, in turn, would alter IGF action.

Circulating insulin-like growth factor II/mannose-6-phosphate receptor and insulin-like growth factor binding proteins in fetal sheep plasma are regulated by glucose and insulin

We have reported previously that levels of insulin-like growth factor I (IGF-I) and IGF-II in fetal sheep plasma decrease with maternal starvation and increase following an infusion of glucose to the starved fetus, while a fetal infusion of insulin elevates UGF-I alone. We now report the changes in the circulating IGF-II/M6P receptor and plasma IGF binding proteins (IGFBPs), as measured by western blotting and ligand blotting, respectively, in fetus and mother during this study. In fetal plasma, the circulating IGF-II/mannose-6-phosphate (M6P) receptor, IGFBP-3 and IGFBP-4 were reduced during starvation. While circulating IGF-II/M6P receptor and IGFBP-4 levels were increased following the fetal insulin or glucose infusion, IGFBP-3 was unchanged and increased only after 48 h of maternal refeeding. Both IGFBP-1 and IGFBP-2 increased with starvation but while IGFBP-1 levels returned to control values following both insulin and glucose infusion, levels of IGFBP-2 were not reduced significantly by either infusion or by refeeding. In maternal plasma, levels of IGFBP-3 and IGFBP-4 decreased while IGFBP-1 and IGFBP-2 increased after 48 h of starvation. Levels of each IGFBP were unaltered following the fetal infusions but returned to values obtained during the control period after refeeding. These data show that each of the IGF carrier proteins is sensitive of changes in nutrition, either acutely, such as IGFBP-1, or chronically, as for IGFBP-3. This suggests that the circulating IGF-II/M6P receptor and the IGFBP's may modulate IGF activity in the fetus during different nutritional states.

Effect of tumor necrosis factor-alpha on the expression of insulin-like growth factor I and insulin-like growth factor binding protein 4 in mouse osteoblasts

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine produced by immune cells, which has multiple effects on bone cells and is therefore thought to mediate changes in bone metabolism occurring during inflammation. In the present study we have investigated the effect of TNF-alpha on the secretion of insulin-like growth factor I (IGF-I) and IGF binding protein 4 (IGFBP-4) by clonal mouse osteoblasts (MC3T3-E1 cells) using subconfluent in vitro cultures and serum-free conditions. The IGF-I was determined by radioimmunoassay under conditions eliminating the interference of IGFBPs. Treatment of MC3T3-E1 cultures with TNF-alpha for 24 h resulted in a dose-dependent decrease in IGF-I secretion (maximally to 34 +/- 9.7% of control with 60 pmol/l TNF-alpha; mean +/- SD). The TNF-alpha treatment also resulted in decreased messenger ribonucleic acid (mRNA) levels of IGF-I at 4 and 24 h, as detected by Northern analysis. Because basal secretion of IGFBPs is very low in MC3T3-E1 cells, effects of TNF-alpha on IGFBP secretion were studied in cultures in which IGFBP-4 expression was increased by calcitriol (1,25(OH)2D3) treatment. The presence of TNF-alpha (600 pmol/l) inhibited this calcitriol-induced stimulation of IGFBP-4 mRNA levels from 4 h onwards, with complete inhibition of the calcitriol effect occurring at 24 h. We also observed a dose-dependent inhibition of calcitriol-stimulated IGFBP-4 secretion into the culture medium (as detected by Western ligand blot), with the maximal inhibition occurring with 600 pmol/l TFN-alpha to 25 +/- 7% of control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning of mouse insulin-like growth factor binding protein 4 (IGFBP4) cDNA and expression of a fusion protein with IGF-binding activity

The TC-1 bone marrow stromal cell line expresses a 2.3 kb IGFBP-4 mRNA transcript. Reverse transcription/polymerase chain reaction was used to amplify the complete open reading frame of the insulin-like growth factor binding protein-4 (IGFBP-4) from poly(A)+ of a murine bone marrow stromal cell line (TC-1). Sequence analysis reveals that the murine IGFBP-4 is highly homologous to the rat IGFBP-4 and less so to the human IGFBP-4. The inferred amino acid sequence has a molecular weight of 25.7 kD. An IGFBP-4/maltose binding protein fusion peptide expression in the pMal-p2 vector produced a fusion protein exhibiting both IGFBP immunoreactivity and IGF-I binding activity with specificity characteristic of IGFBPs.

Reduction of insulin-like growth factor-I (IGF-I) in protein-restricted rats is associated with differential regulation of IGF-binding protein messenger ribonucleic acids in liver and kidney, and peptides in liver and serum

To investigate the influence of the insulin-like growth factor binding-proteins (IGFBPs) on the nutritional regulation of IGF-I's actions, we compared the gene expression of IGF-I and the six IGFBPs in liver and kidney of protein-restricted (P5) and normally fed (P15) young rats. Using poly(A)+ Northern blot analysis, we observed a decrease in IGF-I messenger RNA (mRNA) at steady state in liver (-50%) and kidney (-60%). The increases in IGFBP-1 mRNA were parallel in these two tissues (liver, 5.7-fold; kidney, 4-fold). In contrast, the expression of the other IGFBP genes exhibited organ-specific regulation during protein restriction; although IGFBP-2 mRNA increased in liver in the P5 group (3-fold), it decreased slightly in kidney (-15%). IGFBP-3 mRNA declined by 30% in liver and was unchanged in kidney. IGFBP-4 mRNA increased by 50-88% in liver and was not modified in kidney. IGFBP-5 mRNA was not detected in liver and was identical in kidney of P15 and P5 rats. IGFBP-6 mRNA was not changed in either liver or kidney during protein restriction. To determine whether the changes in IGFBP mRNAs induced by protein restriction were associated with changes in the respective peptides, IGFBPs in supernatants of liver homogenates and in serum of the same rats were measured by ligand blot analyses. IGFBP-1 and IGFBP-2 Western immunoblot analyses were also performed in serum. By ligand blot, a 45,000 mol wt (M(r)) band (IGFBP-3) decreased in liver and serum of P5 rats, paralleling the changes in liver IGFBP-3 mRNA. A 30,000 M(r) band, consistent with IGFBP-1 and/or IGFBP-2, increased in liver. By immunoblot in serum, IGFBP-1 was only detectable in P5 rats, whereas IGFBP-2 decreased in the P5 group. By ligand blot, a 24,000 M(r) band (IGFBP-4) declined slightly in serum (not detected in liver). Our study shows that protein restriction regulates the expression of four of six IGFBPs in rats, and this regulation is organ specific. The nutritional regulation of IGFBP peptides in biological fluids, in particular serum, seems to involve additional mechanisms.

Expression and down-regulation by retinoic acid of IGF binding protein-2 and -4 in medium from human neuroblastoma cells

Insulin-like growth factors (IGFs) regulate the autocrine/paracrine growth of neuroblastomas. The IGFs bind to specific binding proteins (IGFBPs) which modulate their biological activity. We investigated, by Western ligand blotting (WLB), the presence of IGFBPs and their possible modulation by retinoic acid (RA), IGF-I, IGF-II and truncated Des(1-3)IGF-I in conditioned medium (CM) of the human neuroblastoma SK-N-BE(2) cell line. We demonstrated the presence of two IGFBPs, with MW 37 kDa and 25 kDa. Following immunoprecipitation, they turned out to be IGFBP-2 and -4, respectively. The RA-induced differentiation in SK-N-BE(2) cells was accompanied by a marked reduction of the intensity of both IGFBP bands after 48 h (32% and 24% of control, respectively) and 72 h (2% and 0% of control, respectively) incubation. The addition of exogenous IGFs, which did not induce cell differentiation, did not change the IGFBP pattern significantly, except for the truncated form of IGF-I, which induced a marked decrease in both the 37 kDa and 25 kDa bands after 72 h incubation (45% and 18% of control, respectively). These findings suggest that IGFBPs have a role in RA-induced differentiation in human neuroblastoma cells.