Intact IGF-binding protein-4 and -5 and their respective fragments isolated from chronic renal failure serum differentially modulate IGF-I actions in cultured growth plate chondrocytes.

Impairment of longitudinal growth among children with chronic renal failure (CRF) may be partly attributable to the inhibition of insulin-like growth factor (IGF) activity by an excess amount of high-affinity IGF-binding proteins (IGFBP). Elevated levels of immunoreactive IGFBP-4 in CRF serum are inversely correlated with the standardized heights of these children, whereas levels of IGFBP-5, which circulates mainly as proteolyzed fragments, are positively correlated with growth parameters. To delineate the respective effects of these IGFBP on growth cartilage, the biologic effects of intact and fragmented forms of IGFBP-4 and IGFBP-5 on rat growth plate chondrocytes in primary cultures were characterized. Intact IGFBP-4 and IGFBP-5 and the amino-terminal fragment IGFBP-5(1-169) were recombinant proteins; the carboxy-terminal fragments IGFBP-5(144-252) and IGFBP-4(136-237) and the amino-terminal fragment IGFBP-4(1-122) were purified to homogeneity from CRF hemofiltrates. Intact IGFBP-4 and, to a lesser extent, IGFBP-4(1-122) inhibited IGF-I-induced cell proliferation. In contrast, intact IGFBP-5 was stimulatory in the absence or presence of exogenous IGF-I, whereas the amino-terminal fragment IGFBP-5(1-169) was inhibitory. Studies on the mechanism by which IGFBP-4 and IGFBP-5 exert opposite effects on chondrocyte proliferation demonstrated that intact IGFBP-4 prevented the binding of (125)I-IGF-I to chondrocytes, whereas intact IGFBP-5 enhanced ligand binding and was able to bind specifically to the cell membrane. These data suggest that intact IGFBP-4 and, to a lesser extent, IGFBP-4(1-122) act exclusively as growth-inhibitory binding proteins in the growth cartilage. IGFBP-5, however, can either stimulate (if it remains intact) or inhibit (if amino-terminal forms predominate) IGF-I-stimulated chondrocyte proliferation.     

The multi-functional role of insulin-like growth factor binding proteins in bone

The insulin-like growth factor (IGF) system is an important regulator of bone formation. The IGFs (IGF-I and IGF-II) are the most abundant growth factors produced by bone, and are regulated by their six high affinity binding proteins (IGFBPs). The IGFBPs are produced by osteoblasts and are responsible for transporting the IGFs and extending their half-lives. In general, IGFBP-1, -2, -4, and -6 inhibit and IGFBP-3 and –5 stimulate osteoblast function. IGFBP-4 and -5 are the most abundant IGFBPs produced by osteoblasts, and therefore they are the primary focus of this review. IGFBP-5 is an important stimulator of bone formation and may also function independently of IGFs. IGFBP-4 inhibits osteoblast function by sequestering IGF and preventing it from binding to its receptor. This review focuses on the specific IGF-dependent and IGF-independent roles of the IGFBPs in bone formation, as well as their potential mechanisms of action. In addition, discussion of the regulation of the IGFBPs by post-translational modification (i.e., proteolysis) has been included. Studies on the regulation of production and actions of IGFBPs suggest that the IGFBP system in bone is pleiotropic and capable of serving multiple effector inputs from systemic and local sources.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany     

Insulin-like growth factor binding proteins as growth inhibitors in children with chronic renal failure

Children with chronic renal failure (CRF) often fail to attain an adult height consistent with their genetic potential. The growth hormone (GH)/insulin-like growth factor (IGF)/growth plate chondrocyte axis has been intensively studied in these children to determine the basis for this growth failure. Evidence suggests that hepatic GH resistance results in deficient expression of IGF-I. However, serum IGF-I levels are usually normal and it is IGF-I action on target tissues which is inhibited, possibly by the presence of excess high-affinity IGF binding proteins (IGFBPs) in CRF serum. In this paper we evaluate the roles of IGFBP-1, -2, and -3 as growth inhibitors in CRF children. The data support a role for each of these IGFBPs as growth inhibitors. Currently, IGFBP-1 meets most criteria expected of a growth inhibitor, but IGFBP-2 and -3 will likely also meet these criteria and may well be important contributors to the growth failure of CRF. Ultimately, many or all of the six IGFBPs may be found to contribute to the excess high-affinity IGF binding sites which are a hallmark of CRF serum and are possible contributors to the growth failure of CRF children.     

Growth hormone/insulin-like growth factor system in children with chronic renal failure

Disturbances of the somatotropic hormone axis play an important pathogenic role in growth retardation and catabolism in children with chronic renal failure (CRF). The apparent discrepancy between normal or elevated growth hormone (GH) levels and diminished longitudinal growth in CRF has led to the concept of GH insensitivity, which is caused by multiple alterations in the distal components of the somatotropic hormone axis. Serum levels of IGF-I and IGF-II are normal in preterminal CRF, while in end-stage renal disease (ESRD) IGF-I levels are slightly decreased and IGF-II levels slightly increased. In view of the prevailing elevated GH levels in ESRD, these serum IGF-I levels appear inadequately low. Indeed, there is both clinical and experimental evidence for decreased hepatic production of IGF-I in CRF. This hepatic insensitivity to the action of GH may be partly the consequence of reduced GH receptor expression in liver tissue and partly a consequence of disturbed GH receptor signaling. The actions and metabolism of IGFs are modulated by specific high-affinity IGFBPs. CRF serum has an IGF-binding capacity that is increased by seven- to tenfold, leading to decreased IGF bioactivity of CRF serum despite normal total IGF levels. Serum levels of intact IGFBP-1, -2, -4, -6 and low molecular weight fragments of IGFBP-3 are elevated in CRF serum in relation to the degree of renal dysfunction, whereas serum levels of intact IGFBP-3 are normal. Levels of immunoreactive IGFBP-5 are not altered in CRF serum, but the majority of IGFBP-5 is fragmented. Decreased renal filtration and increased hepatic production of IGFBP-1 and -2 both contribute to high levels of serum IGFBP. Experimental and clinical evidence suggests that these excessive high-affinity IGFBPs in CRF serum inhibit IGF action in growth plate chondrocytes by competition with the type 1 IGF receptor for IGF binding. These data indicate that growth failure in CRF is mainly due to functional IGF deficiency. Combined therapy with rhGH and rhIGF-I is therefore a logical approach.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany     

Characterization of insulin-like growth factors and their binding proteins in peritoneal dialysate

.Serum insulin-like growth factors (IGFs), which circulate bound to specific IGF binding proteins (IGFBPs), must exit the intravascular space before acting on target tissues. Little is known about the nature of IGF/IGFBPs in extravascular fluids of patients with chronic renal failure (CRF). Peritoneal dialysate (PD) was studied since, after a short incubation, PD contains proteins which have entered an extravascular space; thus, IGF/IGFBP forms in PD are more likely than serum forms to interact with target tissues. IGF-I and IGF-II, and IGFBPs 1 – 4, were readily identified by specific immunoassays and/or ¹²⁵iodine-IGF ligand blotting of simultaneously obtained PD and serum samples from seven CRF children; IGFBP-3 was a major IGFBP in PD as in serum. Where quantitated, IGF and IGFBP levels in PD were approximately 10% of serum concentrations. After separation of PD and serum by size-exclusion chromatography, serum had more IGFBP-3 in 150-kilodalton (kDa) than 35-kDa fractions, while PD had far less IGFBP-3 in 150-kDa than 35-kDa fractions. Immunoblot studies revealed a major 29-kDa IGFBP-3 fragment, in addition to intact 41- and 38-kDa IGFBP-3 forms, in PD and CRF serum; the 29-kDa form predominated in the 35-kDa PD fractions. These data suggest that the 29-kDa fragment is the IGFBP-3 form most likely to modulate IGF effects on target tissues of CRF individuals. Received: April 17, 1995; received in revised form September 19, 1995; accepted October 12, 1995     

Functional consequences of IGFBP excess—lessons from transgenic mice

The functions of insulin-like growth factor-binding proteins (IGFBPs) have been studied extensively in vitro, revealing IGF-dependent and also IGF-independent effects on cell growth, differentiation, and survival. In contrast, the biological relevance of IGFBPs in vivo is only partially understood. In the past decade, mouse models lacking or overexpressing specific IGFBPs have been generated by transgenic technology. Phenotypic analysis revealed features that are common for most IGFBPs (growth inhibition), but also effects that appear to be specific for some but not all IGFBPs, such as disturbed glucose homeostasis (IGFBP-1 and -3) or impaired fertility (IGFBP-1, -5, and -6). Future systematic comparison of IGFBP functions in transgenic mice will be facilitated by targeted insertion of IGFBP expression vectors and by standardized phenotype assessment. Furthermore, analysis of IGFBP expression in growth-selected mouse lines or pedigrees segregating for growth phenotypes will be important to understand the roles of IGFBPs in multigenic growth regulation.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany     

Fibronectin fragments upregulate insulin-like growth factor binding proteins in chondrocytes

Addition of fibronectin fragments (Fn-fs) to cultured cartilage explants has been shown to mediate extensive cartilage matrix degradation followed by anabolic responses. OBJECTIVE: To determine whether specific Fn-fs regulate cartilage metabolism through a mechanism, in part, involving insulin-like growth factor (IGF) and insulin-like growth factor binding proteins (IGFBPs). METHODS: Primary bovine articular chondrocyte cultures were treated with Fn-fs. mRNA from the cultures was analysed by Northern blotting. Changes in the levels of IGFBPs in cellular extracts and conditioned media were analysed by Western ligand blotting. Explant cultures of bovine articular cartilage were used to assay release of exogenous IGF-I and IGFBP-2. An analog of IGF-I with altered affinity for IGFBPs was used to assay the effect of IGFBPs on proteoglycan synthesis. RESULTS: The Fn-fs increased protein levels of IGFBPs-2, -3 and -5 in conditioned media and of IGFBP-2 in cell extracts by as much as nine-fold. Conversely, the protein level of constitutively expressed IGBP-4 was decreased in conditioned medium. Northern blot analysis reflected increased IGFBP-3 mRNA but not decreased IGFBP-4 mRNA. The IGF-I analog was more effective at restoring PG synthesis suppression by Fn-fs than was wild type IGF-I. CONCLUSIONS: The Fn-fs increased levels of IGFBPs in cultures of bovine articular chondrocytes and elicited release of IGFBP-2 and IGF-I from articular cartilage. The increased level of IGFBPs may trap IGF-I and account in part for the initial suppression of PG synthesis. Induced proteinases may subsequently liberate IGF-I and cause greatly enhanced anabolic processes, contributing to cartilage repair.     

Role of insulin-like growth factor binding proteins in 1alpha,25-dihydroxyvitamin D(3)-induced growth inhibition of human prostate cancer cells

BACKGROUND: The mechanisms underlying 1alpha,25-dihydroxyvitamin D(3) (1,25D)-induced growth inhibition of human prostate cancer cells have not been fully elucidated. To determine whether alterations in the insulin-like growth factor (IGF) signaling axis are associated with 1,25D-induced growth inhibition, we examined the ability of 1,25D to regulate expression of IGF binding proteins (IGFBPs) in human prostate cancer cell lines. METHODS: Northern and Western blot analyses were used to detect 1,25D-induced alterations in IGFBP expression. Additional in vitro studies were performed to determine the role of IGFBP-3 in 1,25D-induced growth inhibition. RESULTS: 1,25D decreased mRNA levels of the growth stimulatory IGFBP-2 and induced IGFBP-3 mRNA in LNCaP and C4-2 cells. 1,25D treatment also increased secreted IGFBP-3 protein levels in prostate cancer cell lines sensitive to 1,25D growth inhibition but had little effect on IGFBP-3 expression in 1,25D-resistant DU145 cells. However, recombinant IGFBP-3 had only a minor effect on LNCaP cell growth in the presence of serum. Furthermore, siRNA duplexes that reduced IGFBP-3 expression did not alter 1,25D growth inhibition in either LNCaP or PC-3 cell lines grown in serum-containing media. CONCLUSIONS: Our studies indicate 1,25D-induced up-regulation of IGFBP-3 is not required for the growth inhibitory effects of 1,25D in prostate cancer cells grown in serum-containing media.     

Insulin-like growth factor binding protein-3 protease activity in the urine of children with chronic renal failure

The insulin-like growth factors, IGF-1 and IGF-II, are polypeptides that potentiate cellular growth. In addition to binding to specific cell surface receptors, the IGFs bind with high affinity to a family of proteins, the insulin-like growth factor binding proteins (IGFBPs). Serum and urine IGFBP patterns are altered in individuals with chronic renal failure (CRF). We recently reported that the urinary IGFBP pattern of CRF patients is unique for increased insulin-like growth factor binding protein-1 (U-IGFBP-1) levels. In this study, we used western ligand blotting (WLB), western immunoblotting (WIB), and radioimmunoassay (RIA) to further evaluate serum and urine IGFBP profiles of children with CRF (n=14). Five patients with CRF displayed decreased serum IGFBP-3 profiles by WLB. Serum IGFBP-3 WIB profiles were remarkable for 30- and 20-kDa fragments of IGFBP-3 not seen in control serum. Serum IGFBP-3 levels, as determined by RIA, were slightly elevated. Serum levels of IGFBP-2 also were increased, although not at a level reaching statistical significance. WLB of CRF urine revealed a large increase in U-IGFBP-1 and a complete absence of urinary IGFBP-3. Recent studies of serum from pregnant women and seminal plasma have demonstrated a similar absence of intact IGFBP-3, due to the presence of a specific IGFBP-3 protease. To evaluate whether an IGFBP-3 protease accounts for the absence of intact U-IGFBP-3 in children with CRF, urine and serum samples from individuals with CRF and controls were tested. An IGFBP-3 protease assay using concentrated urine revealed the presence of two distinct proteases found only in the CRF urines. Serum IGFBP-3 protease activity was no greater in patients with CRF than in controls. We conclude that the decrease in intact urinary IGFBP-3 is due to proteolysis by an IGFBP-3 protease.     

Serum insulin-like growth factor binding protein (IGFBP)-4 and IGFBP-5 in children with chronic renal failure: relationship to growth and glomerular filtration rate

Growth retardation in children with chronic renal failure (CRF) is partly due to an inhibition of insulin-like growth factor (IGF) activity by an excess of high-affinity IGF-binding proteins (IGFBPs). The aim of this study was to analyze the serum levels and forms of IGFBP-4 and IGFBP-5 in CRF patients using specific, recently developed radioimmunoassays (RIAs) and immunoblot analysis. We examined 89 children [age 11.5 (2.8–19.0) years] with CRF [glomerular filtration rate 26.6 (7.0–67.4) ml/min per 1.73 m²], nine of them with end-stage renal disease undergoing peritoneal dialysis. Serum-immunoreactive IGFBP-4 levels were fourfold increased in CRF (prepubertal 1080±268 ng/ml; pubertal 989±299 ng/ml) compared to healthy prepubertal controls (265±73 ng/ml). In contrast, serum IGFBP-5 levels were not significantly increased neither in prepubertal (361±120 ng/ml vs 282±75 ng/ml in controls) nor pubertal CRF children (478±165 ng/ml vs 491±80 ng/ml in controls). Immunoblot analysis showed the presence of intact as well as fragmented IGFBP-4 and IGFBP-5. Serum IGFBP-4, but not IGFBP-5, levels were inversely correlated with GFR (r=–0.39, P<0.001). In prepuber- tal children, IGFBP-4 levels were inversely correlated with standardized height (r=–0.40; P<0.005). In contrast, IGFBP-5 levels were positively correlated both with standardized height (r=0.32, P<0.02) and baseline height velocity (r=0.45, P<0.005). A 3-month therapy with rhGH stimulated serum IGFBP-5 levels by 43% (P<0.01); there was no consistent effect on IGFBP-4 levels. There was a positive correlation between IGFBP-4 and IGFBP-2 (r=0.46, P<0.001); IGFBP-5 was positively correlated with IGF-I (r=0.59, P<0.001), IGF-II (r=0.42, P<0.001) and IGFBP-3 (r=0.47, P<0.001) and inversely correlated with IGFBP-1 (r=–0.41, P<0.001). In summary, serum IGFBP-4 is fourfold elevated in children with CRF in relation to the degree of renal dysfunction and contributes to the marked increase in IGF-binding capacity in CRF serum. The inverse correlation of serum IGFBP-4 with standardized height is consistent with its role as another inhibitor of the biological action of the IGFs on growth plate cartilage. In contrast, serum IGFBP-5 is not elevated in CRF serum and circulates mainly as proteolysed fragments. The positive correlation of serum IGFBP-5 with growth and its increase during GH therapy indicate that IGFBP-5 is a stimulatory IGFBP in patients with CRF, either by enhancing IGF activity through better presentation of IGF to its receptor or by an IGF-independent effect through activation of a specific, recently described putative IGFBP-5-receptor. Received: 24 September 1999 / Revised: 6 January 2000 / Accepted: 13 January 2000 / Accepted: 13 January 2000     

Expression of insulin-like growth factor binding proteins in healing tendon lesions.

he treatment of overuse tendon injuries with exogenous growth factors such as insulin-like growth factor-I (IGF-I) may facilitate an improved return to sustained athletic function. The biological effects of IGF-I are exerted under the control of a complex of IGF receptors, binding proteins, and proteases. This IGF system includes a family of six structurally related high-affinity IGF binding proteins (IGFBPs) that protect IGF-I from local proteases and restrict access of IGF-I to its receptor. This study describes the expression of the IGFBPs in flexor tendon after acute injury and during healing over time. Collagenase-induced lesions were created in the tensile region of the flexor digitorum superficialis tendon of both forelimbs of 14 horses. Tendons were harvested from euthanatized horses 1, 2, 4, 8, or 24 weeks following injury. Gene expression was quantitated by fluorescent real-time PCR, and protein expression was evaluated by Western ligand blot (WLB). Message for IGFBPs 2 to 6 was expressed in both normal and healing tendon. No IGFBP-1 mRNA was detected in equine tendon. Message expression for IGFBP-2, -3, and -4 increased following injury, whereas message expression for IGFBP-5 and -6 decreased. Protein expression for IGFBP-2, -3, and -4 was detected by WLB in normal tendon and showed a marked increase following injury. Protein for IGFBP-5 and -6 was not detectable by WLB in normal or healing tendon. The results of this study document the IGFBP response of flexor tendons to injury and healing, which provides information necessary for the design of protocols that may enhance tendon healing through manipulation of IGF-I ligand and binding protein levels.     

IGF-binding protein-3 fragments in plasma of a child with acute renal failure

The insulin-like growth factors (IGF) -I and -II promote cellular growth and differentiation of various organs. Their growth-stimulating effects are modulated by a family of six IGF-binding proteins (IGFBPs). Altered patterns of intact and fragmented IGFBPs have been reported in serum and urine of children with chronic renal failure (CRF), and it has been suggested that this may contribute to the growth failure observed in these patients. In the present study, a rapid and comprehensive method is presented to analyze IGFBPs and IGFBP fragments in the plasma of a child with acute renal failure (ARF) who had undergone plasmapheresis. The plasma IGF-I and IGFBP-3 levels were drastically reduced. Plasmapheresis filtrate (3 l) was fractionated by cation-exchange chromatography and reversed-phase high-performance liquid chromatography. The fractions obtained were tested by ligand and immunoblotting. In addition to IGFBP-1 and -4 fragments, the majority of IGF-binding polypeptides were IGFBP-3 immunoreactive. N-terminal sequence analysis of a 17-kDa polypeptide revealed the isolation of a C-terminal fragment of IGFBP-3 starting with Lys 160. The IGF-II-binding polypeptide pattern in the ARF plasma resembles the pattern in hemofiltrate from CRF patients, suggesting that similar or identical proteases are involved in IGFBP-3 fragmentation and common mechanisms may lead to the accumulation of the fragments in both diseases.     

Enhanced expression of insulin-like growth factor-binding proteins in human osteoarthritic cartilage detected by immunohistochemistry and in situ hybridization

OBJECTIVE: To determine the roles of insulin-like growth factor (IGF) and IGF-binding protein (IGFBP) in the pathogenesis of osteoarthritis (OA). DESIGN: Cartilage tissues were obtained from the femoral heads of patients with OA, and those from patients with femoral neck fractures were used as a control. The expression of IGFBP-3, -4, and -5 was examined using immunohistochemistry and in situ hybridization, and IGF-I and IGF-I receptors were also immunohistochemically detected. The percentages of positive chondrocytes were determined by counting the total number of chondrocytes over the area of the surface, middle, and deep zones of the cartilage. RESULTS: There was a marked increase in the percentage of positive chondrocytes in all IGFBPs on protein and messenger RNA levels for OA compared to that of the control cartilage. Furthermore, enhanced expression of IGFBPs and the IGF-I/IGF-I receptor was positively correlated with the histologic score for cartilage lesions. CONCLUSION: Up-regulation of IGFBPs as well as IGF-I and its receptor was observed for OA cartilage tissue, suggesting the involvement of IGFBPs in the pathogenesis of OA.     

Preferential expression of insulin-like growth factor binding proteins-1, -3, and -5 during early diabetic renal hypertrophy in rats

The renal insulin-like growth factor-I (IGF-I) system has been implicated in the pathogenesis of renal hypertrophy, altered hemodynamics, and extracellular matrix expansion associated with early diabetes. The relative abundance of IGF binding proteins (IGFBPs) in the renal microenvironment may modulate IGF-I actions. However, the precise IGFBPs expressed in the glomerular and tubulointerstitial compartments during diabetic renal growth have not been characterized. In the present study, in situ hybridization studies were performed to examine the expression of IGFBP-1 to -6 messenger RNAs (mRNAs) 3, 7, and 14 days after streptozotocin (STZ) injection in rats. In control, nondiabetic kidneys, all six IGFBP mRNAs were differentially expressed with a predominance of IGFBP-5. The onset of renal hypertrophy in STZ-induced diabetes was associated with a rapid and site-specific induction of IGFBP-1, -3, and -5 mRNAs. In contrast, basal expression of IGFBP-2, -4, and -6 mRNAs was not altered in diabetic rats. IGFBP-5 mRNA expression increased in diabetic glomeruli, cortical, and inner medullary peritubular interstitial cells at days 3, 7, and 14. Although normal glomeruli failed to express IGFBP-3, it was induced concomitantly with IGFBP-5 in diabetic glomeruli and cortical peritubular interstitial cells. IGFBP-1 mRNA levels also increased in cortical tubular cells at each time point tested. Peak induction of IGFBP-3 and -5 was observed at day 3, whereas IGFBP-1 was delayed until day 7. IGFBP-1, -3, and -5 mRNA levels declined by day 14, but remained persistently elevated above control. By immunoperoxidase staining, similar alterations in the pattern of IGFBP-3 and -5 protein expression were observed at each time point. The preferential and site-specific increase in IGFBP-1, -3, and -5 suggest that these IGFBPs may regulate the local autocrine and/or paracrine actions of IGF-I and contribute to the pathogenesis of the early manifestations of diabetic nephropathy.     

DIFFERENTIAL EXPRESSION OF INSULIN-LIKE GROWTH FACTOR BINDING PROTEINS IN HIGH VERSUS LOW GLEASON SCORE PROSTATE CANCER

Purpose

The insulin-like growth factor (IGF) system appears to be important in human prostate cancer biology. Expression of specific IGF binding proteins (IGFBPs) by prostate cancer tissues may modulate IGF cellular actions, and possibly determine both IGF-dependent tumor growth and biological aggressiveness in vivo. The purpose of this study was to examine the differential expression of all six IGFBP genes in benign and malignant prostate tissue samples.

Materials and Methods

Using RNAse protection assays, we examined expression of IGFBPs 1 through 6 in 23 paired benign and neoplastic prostate tissue samples obtained from the same prostatectomy specimen. RNA expression levels on each tissue sample were determined densitometrically and groups compared using standard Student's t test.

Results

We found expression of IGFBPs 2 through 6, but not IGFBP-1, in both malignant and benign tissues. A statistically significant differential expression of IGFBPs 2, 3 and 5 was found between tumors with high Gleason score and those with low scores and benign tissues. Expression of IGFBPs 2 and 5 was higher (p = 0.002 and 0.04, respectively) while that of IGFBP-3 was lower (p = 0.05) in high versus low Gleason score cancer specimens. Expression of IGFBPs 4 and 6 was no different between tumors (p = 0.052 and 0.25, respectively). No significant differences in IGFBP expression were evident between benign and tumor tissues when tumor grade was not considered.

Conclusion

Our results indicate that differential expression of certain IGFBPs in human prostate cancer correlates with tumor Gleason score. Thus, expression of certain IGFBPs in prostate cancer may be used as a surrogate marker of aggressive clinical behavior.     

The insulin-like growth factor system in the prostate

Summary The insulin-like growth factor (IGF) system is involved in the regulation of cell growth. The system involves a network of molecules that includes the IGFs themselves (IGF-I and -II), IGF receptors (types I and II), IGF-binding proteins (IGFBP-1 through -6), and IGFBP proteases. Characterization of this complex system in the prostate has recently been initiated. Prostatic cell lines as well as primary cultures of prostatic epithelial and stromal cells have been analyzed for expression of IGFs, receptors, and IGFBPs. Prostatic epithelial cells and, quite likely, stromal cells as well respond to the mitogenic activity of IGFs via the type I IGF receptor. Prostatic stromal cells synthesize and secrete IGF-II; there is evidence that prostatic cell lines also synthesize IGFs, but this has not been confirmed in primary cultures of prostatic epithelial cells. Prostatic stromal and epithelial cells secrete a number of IGFBPs. The biological impact of some of these IGFBPs on the growth of prostatic cells has been examined, and proteolytic cleavage of IGFBP-3 by prostate-specific antigen (PSA) has been demonstrated. Aberrations in several elements of the IGF system have been observed in stromal cells derived from benign prostatic hyperplasia (BPH). The IGF system may therefore have a part in the etiology of BPH as well as in normal and malignant processes in the prostate.     

Serum insulin-like growth factors and their binding proteins in children with end-stage renal disease

Serum levels of insulin-like growth factor-I (IGF-I), IGF-II, and IGF binding protein-1 (IGFBP-1), IGFBP-2, and IGFBP-3 were measured in 54 children with end-stage renal disease (ESRD). The results were compared with their respective age-dependent normal ranges. IGFs and IGFBPs were quantified by specific radioimmunoassay. Serum IGF-I in children with ESRD tended to cluster in the low-normal range. Mean age-related serum IGF-I levels were slightly, but significantly decreased (–1.08±0.17 SDS). In view of the prevailing elevated growth hormone levels in ESRD, these serum, IGF-I levels must be interpreted as inadequately low. In contrast to IGF-I, individual serum IGF-II levels were either in the uppernormal range or clearly elevated. Mean age-related IGF-II (1.09±0.15 SDS) was lightly, but significantly elevated. Mean age-related IGFBP-1 serum levels (2.20±0.10 SDS) were moderately increased, while mean age-related serum IGFBP-2 (5.65±0.36) and IGFBP-3 levels (3.60±0.19) were markedly elevated. Affinity cross-linking of¹²⁵iodine-IGF-II to sera from patients with ESRD and immunoprecipitation with a specific antiserum showed that low molecular weight IGFBP-3 fragments in ESRD serum are capable of binding IGF. In patients with ESRD, a rapid and persistent decline of immunoreactive IGFBP-3 in response to restoration of renal function by renal transplantation was observed. This finding indicates that renal dysfunction contributes to high immunoreactive, IGFBP-3 levels in ESRD. In conclusion, the imbalance between normal total IGF levels and the excess of IGFBPs in ESRD is likely to play a role in growth failure in these children.     

Thyroid hormone‐mediated growth and differentiation of growth plate chondrocytes involves IGF‐1 modulation of β‐catenin signaling

Thyroid hormone regulates terminal differentiation of growth plate chondrocytes in part through modulation of the Wnt/β‐catenin signaling pathway. Insulin‐like growth factor 1 (IGF‐1) has been described as a stabilizer of β‐catenin, and thyroid hormone is a known stimulator of IGF‐1 receptor expression. The purpose of this study was to test the hypothesis that IGF‐1 signaling is involved in the interaction between the thyroid hormone and the Wnt/β‐catenin signaling pathways in regulating growth plate chondrocyte proliferation and differentiation. The results show that IGF‐1 and the IGF‐ receptor (IGF1R) stimulate Wnt‐4 expression and β‐catenin activation in growth plate chondrocytes. The positive effects of IGF‐1/IGF1R on chondrocyte proliferation and terminal differentiation are partially inhibited by the Wnt antagonists sFRP3 and Dkk1. T₃ activates IGF‐1/IGF1R signaling and IGF‐1‐dependent PI3K/Akt/GSK‐3β signaling in growth plate chondrocytes undergoing proliferation and differentiation to prehypertrophy. T₃‐mediated Wnt‐4 expression, β‐catenin activation, cell proliferation, and terminal differentiation of growth plate chondrocytes are partially prevented by the IGF1R inhibitor picropodophyllin as well as by the PI3K/Akt signaling inhibitors LY294002 and Akti1/2. These data indicate that the interactions between thyroid hormone and β‐catenin signaling in regulating growth plate chondrocyte proliferation and terminal differentiation are modulated by IGF‐1/IGF1R signaling through both the Wnt and PI3K/Akt signaling pathways. While chondrocyte proliferation may be triggered by the IGF‐1/IGF1R‐mediated PI3K/Akt/GSK3β pathway, cell hypertrophy is likely due to activation of Wnt/β‐catenin signaling, which is at least in part initiated by IGF‐1 signaling or the IGF‐1‐activated PI3K/Akt signaling pathway. © 2010 American Society for Bone and Mineral Research