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.(ABSTRACT TRUNCATED AT 250 WORDS)
[Show abstract][Hide abstract] ABSTRACT: The IGFs (-I and -II) are normally found in serum and other extracellular fluids complexed to specific binding proteins (IGFBPs). While several IGFBPs have been identified in vitreous and aqueous humors, the major serum carrier of IGF, IGFBP-3, is notably absent from these fluids. To determine if this paucity could be due to an IGFBP-3 proteinase (IGFBP-3ase), samples of bovine vitreous or aqueous humor were mixed with serum and incubated at 37 degrees C for 4 h followed by western ligand blotting. In these experiments, a distinct loss of the 46 kDa band representing IGFBP-3 was observed while other bands present at 35, 28 and 25 kDa were unaltered. The IGFBP-3ase activity is temperature sensitive, has a pH optimum of about 8.0 and is inhibited by EDTA. Acid treatment of serum to remove endogenously bound IGF does not affect the specificity or activity of the IGFBP-3 proteinase. Size exclusion chromatography of bovine aqueous indicates an approximate molecular weight of 260 kDa. Incubation of recombinant IGFBP-3 or serum with partially-purified IGFBP-3ase results in the appearance of low molecular weight fragments of approximately 30 kDa. These fragments are undetectable by western ligand blotting but are readily visualized using an IGFBP-3 specific antibody. Comparison of normal and diabetic vitreous humor reveals the presence of an increased amount of IGFBP-3 proteolytic fragments in the diabetic as compared to control. These findings indicate the presence of a IGFBP-3 proteinase in aqueous and vitreous humors that may be important in regulating ocular homeostasis.
Current Eye Research 03/1995; 14(2):127-35. DOI:10.3109/02713689508999924 · 1.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The insulin-like growth factors (IGF-I and IGF-II) are small, ~ 7 kDa polypeptide hormones present in many embryonic and adult tissues. Accumulating evidence indicates that they play a fundamental role in regulating embryonic growth and differentiation as well as in maintaining homeostasis in the adult. IGFs are normally found in a complex with specific IGF-binding proteins (IGFBPs) of which six different types have been identified. Classically, IGFBPs were only thought to function as carriers of IGF, extending the half-life of IGF in the circulation. However, recent evidence indicates that IGFBPs are able to enhance or inhibit IGF effects on a number of different cell types and also, by themselves, exert independent effects. In the present article, we provide a brief overview of the IGF system in the eye with particular reference to development. Ocular tissues have now been shown to contain all of the components of this system which consists of the two ligands (IGF-I and IGF-II), membrane receptors, soluble binding proteins (BPs) and BP-specific proteases. Importantly, there is now good evidence for an independent, local regulation of IGFBPs in the vitreous humor of the developing chick. In the eye, IGFBP-2 appears to be the predominant IGFBP. Northern blot and in-situ hybridization studies of IGFBP-2 expression in developing ocular tissues of the chick demonstrate the widespread occurrence of this IGFBP and its differential temporal and spatial expression. The appearance of IGFBP-2 in ocular tissues during critical stages of embryogenesis suggests a role for this IGFBP in development of the cornea, sclera and retina. Recent evidence suggests the presence of BP-specific protease activities in vitreous and aqueous humors that could regulate BP levels in vivo. Finally, a possible role for IGF and its IGFBPs in proliferative diseases such as diabetic retinopathy is discussed.
Progress in Retinal and Eye Research 07/1997; 16(3). DOI:10.1016/S1350-9462(96)00036-5 · 8.73 Impact Factor
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