Plasminogen binds the heparin-binding domain of insulin-like growth factor-binding protein-3

Abstract

Limited proteolysis lowers affinity of insulin-like growth factor (IGF)-binding protein (IGFBP)-3 for bound IGFs, resulting in greater IGF bioavailability. Plasmin is one of many proteases that cleave IGFBP-3, and the plasmin system may regulate IGFBP-3 proteolysis and IGF bioavailability in cultured cells in vitro. A role for the plasmin system in IGFBP-3 proteolysis in vivo is suggested by data presented here showing that IGFBP-3 binds plasminogen (Pg; Glu-Pg) with a dissociation constant ( K d) ranging from 1.43 to 3.12 nM. IGF-I and Glu-Pg do not compete for IGFBP-3 binding; instead, the binary IGFBP-3/Glu-Pg complex binds IGF-I with high affinity ( K d= 0.47 nM) to form a ternary complex. Competitive binding studies suggest that the kringle 1, 4, and 5 domains of Glu-Pg and the heparin-binding domain of IGFBP-3 participate in forming the IGFBP-3/Glu-Pg complex, and other studies show that Glu-Pg in this complex is activated at a normal rate by tissue Pg activator. Importantly, IGFBP-3/Glu-Pg complexes were detected in both human citrate plasma and serum, indicating that these complexes exist in vivo. Binding of IGFBP-3 to Glu-Pg in vivo suggests how Glu-Pg activation can specifically lead to IGFBP-3 proteolysis with subsequent release of IGFs to local target tissues.

Signaling through the Smad Pathway by Insulin-like Growth Factor-binding Protein-3 in Breast Cancer Cells

“…We now report that IGFBP-3 can stimulate phosphorylation of the cell surface receptor TGF-␤RI and activate the promoter of the TGF-␤-responsive gene, PAI-1, which encodes plasminogen activator inhibitor-1 (PAI-1). PAI-1 blocks the activation of plasminogen to plasmin, a protease that causes partial fragmentation of IGFBP-3, thus limiting its ability to inhibit IGF action (15,16). Furthermore, we show that basic residues in the carboxyl-terminal region of IGFBP-3 previously shown to be involved in its cell surface association (17) and nuclear translocation (18) are not involved in IGFBP-3 stimulation of the Smad pathway.…”

“…Although we used the PAI-1 reporter system as a marker of Smad-mediated signaling, the plasmin system in fact appears to be involved in IGFBP-3 regulation in a number of cell types. For example, plasminogen binds to IGFBP-3 in vivo, an interaction proposed to lead to IGFBP-3 proteolysis (15). Plasmin-derived IGFBP-3 fragments can exert both inhibitory and stimulatory effects on cell proliferation and show greatly decreased IGF binding, Thus, plasmin proteolysis of IGFBP-3 can regulate IGF bioavailability (42).…”

Alterations in insulin-like growth factor binding protein-3 proteolysis and complex formation in the arthritic joint

“…-2 antiplasmin complexing with plasmin) or by the association of IGFBP-3 with a distinct inhibitor, or whether IGFBP-3 is conformationally protected from proteolysis is under investigation. It is increasingly evident that IGFBP-3 is able to associate with molecules outside the IGF system (Campbell et al 1998), and this may regulate IGFBP-3 protection from, or susceptibility to, proteolysis (Durham et al 1999). Inhibition of IGFBP-3 proteolysis by 150 kDa column fractions from RASynF and normal adult serum could suggest that there is an inhibitor that is associated with the IGFBP-3 in the 150 kDa complex.…”

Targeting Insulin-Like Growth Factor-I and Insulin-Like Growth Factor–Binding Protein-3 Signaling Pathways. A Novel Therapeutic Approach for Asthma

“…It contains IGF-binding residues (51)(52)(53), and may form an IGF-binding pocket together with the N-terminal domain (10). IGFBP-3 can also bind fibrinogen, fibrin, and plasminogen via this region (54,55). This domain contains a functionally important 18-residue basic motif with heparin-binding activity, and can bind heparin, other glycosaminoglycans, and proteoglycans (56,57).…”