Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.7 (plasmin)
 9,023 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Insulin-like growth factors (IGF-I and IGF-II) in biological fluids bind to high-affinity binding proteins (IGFBP-1 to -6), which transport them and regulate their activities. Limited proteolysis of certain IGFBPs plays a major role in this regulation. IGFBP-3 is proteolysed in vivo and in several cell lines by serine proteases, including plasmin. In earlier studies we reproduced this proteolysis in vitro using recombinant human non-glycosylated IGFBP-3. Two major fragments were obtained, the larger retaining weak affinity for IGF-I and weakly inhibiting IGF I mitogenic effects. The smaller fragment, though lacking affinity for IGFs, is a potent growth inhibitor. These proteolytic fragments were isolated by HPLC and their N-terminal amino acids sequenced. Both major fragments contain the N-terminal region of the intact protein, the larger form corresponding to residues 1-160, and the smaller form, to residues 1-95. Kinetics experiments using the MG-63 osteoblast-like cell line showed that the larger peptide is generated before the smaller peptide, the latter probably being a product of secondary proteolysis of the former. Our data suggest that proteolysis of IGFBP-3 is intimately linked to its biological function. We propose a model for its action at cellular level.
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PMID:Proteolytic fragments of insulin-like growth factor binding protein-3: N-terminal sequences and relationships between structure and biological activity. 933 97

Insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) is known to be secreted as a phosphoprotein, constitutively phosphorylated at casein kinase 2 (CK2) sites. To examine the effect of phosphorylation by CK2 on the properties of glycosylated human IGFBP-3, we phosphorylated plasma-derived IGFBP-3, containing less than 1 mol/mol phosphoserine, in vitro. As judged by incorporated 32P, enzymatic deglycosylation did not decrease the phosphate content of phospho-IGFBP-3. Phosphorylation had no effect on IGF-I or IGF-II binding, but was inhibitory to acid-labile subunit binding in the presence of either IGF. Determined in simian virus 40-transformed human fibroblasts, cell association by phospho-IGFBP-3 was inhibited approximately 50% compared with that of the nonphosphorylated preparation. Phospho-IGFBP-3 showed significant resistance to proteolysis by plasmin and a cysteine protease secreted by MCF-7 cells. However, no difference was seen between the two preparations in their inhibition of IGF-I-stimulated DNA synthesis when coincubated with IGF-I in neonatal skin fibroblasts or MCF-7 breast cancer cells, and little difference was found in their ability to potentiate IGF-I-stimulated DNA synthesis when preincubated with fibroblasts. These results indicate that IGFBP-3 interaction with acid-labile subunit and with the cell surface, both of which involve basic carboxyl-terminal residues, may be modulated by phosphorylation. Relative resistance to proteolysis and poor binding to cells suggest that CK2-phospho-IGFBP-3 may be a significant inhibitor of IGF activity in the extracellular environment.
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PMID:The effect of phosphorylation by casein kinase 2 on the activity of insulin-like growth factor-binding protein-3. 1065 Sep 37

In a previous study, the biphasic effect of increasing dosages of recombinant human insulin-like growth factor binding protein-3 (rhIGFBP-3) on proliferation in the prostate carcinoma PC-3 cell line (stimulation followed by depression) was shown to reflect changes in the bioavailability of IGF-II secreted by the cells, IGF-II being the major factor responsible for their autocrine growth. These changes depend on the extent of IGFBP-3 proteolysis induced by serine proteases, in particular, plasmin. In order to examine the mechanism of action of IGFBP-3, we investigated the effects of its two major fragments isolated by HPLC following limited proteolysis by plasmin in vitro. The predominant fragment with an apparent molecular mass of 22-25 kDa in SDS-PAGE (under non-reducing conditions) had previously been shown to retain weak affinity for IGFs, whereas the other fragment of 16 kDa lost all such affinity. From their recently determined amino acid sequences, these fragments correspond to the first 160 and 95 residues, respectively, of IGFBP-3. 0.5-5 nM intact rhIGFBP-3(1-264), when pre-incubated with 5 nM rhIGF-II, dose-dependently inhibited (up to 100%) its mitogenic effect, via sequestration owing to its strong affinity for IGF-II. The same concentrations of the larger fragment (IGFBP-3(1-160)) elicited only weak inhibition (up to 30%), coherent with its weak affinity. The smaller fragment (IGFBP-3(1-95)) provoked total inhibition despite its lack of affinity for IGFs and therefore by an IGF-independent mechanism. PC-3 cells in serum-free medium were weakly stimulated by 5 nM intact IGFBP-3. This had previously been shown to be related to its proteolysis and the ratio of proteolysed to intact IGFBP-3. At the same concentration, IGFBP-3(1-160) stimulated this proliferation by a factor of 5-7, whereas IGFBP-3(1-95) totally suppressed it. 5 nM IGFBP-3(1-95) inhibited the mitogenic action of 1% fetal calf serum by 80%, but by only 25% in the presence of an antibody blocking the type 1 IGF receptor. Its inhibition is therefore exerted principally, but not exclusively, via the IGF signalling pathway. Our data indicate that the IGFBP-3 fragments composed of residues 1-160 and 1-95 are biologically active on PC-3 cells and that their opposite actions may account for the events observed when IGFBP-3 is proteolysed in the cell environment. These proteolytic fragments may therefore play a role in the development of prostate adenocarcinomas in vivo.
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PMID:Prostate carcinoma (PC-3) cell proliferation is stimulated by the 22-25-kDa proteolytic fragment (1-160) and inhibited by the 16-kDa fragment (1-95) of recombinant human insulin-like growth factor binding protein-3. 1099 Apr 47

The IGF-II/mannose 6-phosphate receptor (IGF2R) function in extracellular matrix (ECM) remodeling is known to occur as a result of transforming growth factor-beta (TGF-beta) activation and plasmin in the proteolytic cleavage level caused by the interaction between latent TGF-beta and urokinase plasminogen activator receptor (uPAR) respectively. In one of our previous studies, we found IGF-II and IGF2R dose-dependently correlated with the progression of pathological hypertrophy remodeling following complete abdominal aorta ligation. However, how this IGF2R signaling pathway responds specifically to IGF-II and regulates the myocardial ECM remodeling process is unclear. We found that IGF2R was aberrantly expressed in myocardial infarction scars. The matrix metalloproteinase-9 (MMP-9) zymographic activity was elevated in H9c2 cardiomyoblast cells treated with IGF-II, but not IGF-I. Treatment with Leu27IGF-II, an IGF2R specifically binding IGF-II analog, resulted in significant time-dependent increases in the MMP-9, tissue-type plasminogen activator (tPA), and urokinase plasminogen activator (uPA); and a reduction in the tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) protein expression. Furthermore, IGF2R expression inhibition by siRNA blocked the IGF-II-induced MMP-9 activity. We hypothesize that after IGF-II is bound with IGF2R, the resulting signal disrupts the balance in the MMP-9/TIMP-2 expression level and increases plasminogen activator (PAs) expression involved in the development of myocardial remodeling. If so, IGF2R signaling inhibition may have potential use in the development of therapies preventing heart fibrosis progression.
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PMID:IGF-II/mannose 6-phosphate receptor activation induces metalloproteinase-9 matrix activity and increases plasminogen activator expression in H9c2 cardiomyoblast cells. 1849 91


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