Interaction of Insulin-like Growth Factor II (IGF-II) with Multiple Plasma Proteins

Abstract

In the circulation, most of the insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs), and IGFBP proteases are bound in high molecular mass complexes of >150 kDa. To investigate molecular interactions between proteins involved in IGF⅐IGFBP complexes, Cohn fraction IV of human plasma was subjected to IGF-II affinity chromatography followed by reversed-phase high pressure liquid chromatography and analysis of bound proteins. Mass spectrometry and Western blotting revealed the presence of IGFBP-3, IGFBP-5, transferrin, plasminogen, prekallikrein, antithrombin III, and the soluble IGF-II/mannose 6-phosphate receptor in the eluate. Furthermore, an IGFBP-3 protease cleaving also IGFBP-2 but not IGFBP-4 was co-purified from the IGF-II column. Inhibitor studies and IGFBP-3 zymography have demonstrated that the 92-kDa IGFBP-3 protease belongs to the class of serine-dependent proteases. IGF-II ligand blotting and surface plasmon resonance spectrometry have been used to identify plasminogen as a novel high affinity IGF-II-binding protein capable of binding to IGFBP-3 with 50-fold higher affinity than transferrin. In combination with transferrin, the overall binding constant of plasminogen/transferrin for IGF-II was reduced 7-fold. Size exclusion chromatography of the IGF-II matrix eluate revealed that transferrin, plasminogen, and the IGFBP-3 protease are present in different high molecular mass complexes of >440 kDa. The present data indicate that IGFs, low and high affinity IGFBPs, several IGFBP-associated proteins, and IGFBP proteases can interact, which may result in the formation of binary, ternary, and higher molecular weight complexes capable of modulating IGF binding properties and the stability of IGFBPs. The insulin-like growth factors (IGF-I and IGF-II)1 are important regulators of growth, differentiation, and survival.Both their mitogenic and metabolic effects are for the most part mediated through binding and activation of the IGF-I receptor (1). The interaction of IGFs with the IGF-I receptor is controlled by a family of six high affinity IGF-binding proteins (IGFBP-1 to IGFBP-6) exhibiting strong sequence homology. The cysteine-rich N-and C-terminal domains are conserved across all IGFBPs, and both domains appear to be involved in IGF binding (2, 3). In the circulation, the majority of the IGFs are sequestered into ternary 150-kDa complexes with either IGFBP-3 or IGFBP-5 and the 85-kDa acid-labile subunit, prolonging the half-life of IGFs, controlling their transcapillary transport to the target tissues, and functioning as a circulating reservoir of IGFs (4 -6). The IGFBPs can also form binary complexes with IGFs. Limited proteolysis of IGFBPs appears to be the major mechanism for the release of IGFs from binary and ternary IGFBP complexes, resulting in the generation of IGFBP fragments with reduced affinities for IGFs (7,8). Several cation-and serine-dependent serum proteases, such as a disintegrin and metalloprotease (ADAM) 12S, matrix metalloprotease-3, ␣-kallikrein, plasmin, thrombin, and the...

The IGF-II–Insulin Receptor Isoform-A Autocrine Signal in Cancer: Actionable Perspectives

“…The IGFBPs 1-7 and 9. Insulin-like growth factor-II has been shown to bind to most of the soluble extracellular proteins of the IGFBP family, as reviewed elsewhere [49][50][51]. The cumulative effect of IGF-II binding proteins towards the IGF-II levels in the bloodstream might mitigate its increased exposure to local tissues.…”

“…Transferrin (TF). TF has been shown to be a constitutive component of the 150kDa trimeric IGF binding protein complex found in the bloodstream [51]. Its binding to IGFs (I and II) is less strong than other IGF-IGFBP interactions (where the highest affinity is shown with IGFBP3), and its physiological role is still to be determined.…”

The Role of Insulin-Like Growth Factor Binding Proteins

“…No specific cell surface receptors have been described for the related CCN proteins, but it is now recognised that they generally act via integrin receptors with which they interact through non-classical recognition sequences [36]. Similarly, although IGFBP-3 and IGFBP-5 do not possess classical integrin recognition sequences, IGFBP-3 has been reported to associate with the β 1 integrin [35, 37], and IGFBP-3 and IGFBP-5 are know to bind with high affinity to many known integrin ligands such as fibrin, fibrinogen [38], fibronectin [39], ADAM-12 [40], plasminogen [41], thrombospondin and osteopontin [42], and to caveolin-1 and the transferrin receptor [37, 43]. It is possible that these IGFBPs interact with integrin receptors via one of these intermediates or directly via a non-classical integrin recognition sequence.…”

Loss of androgen receptor promotes adipogenesis but suppresses osteogenesis in bone marrow stromal cells

“…In order to determine whether the pAkt is regulated by AR mediated IGFBP3 signaling, the IGF2 inhibitor (Chromeceptin) was used to mask AR effects (Ma et al, 2011), since it has been shown that IGF2 is regulated by IGFBP3. We found pAkt is increased in ARKO BMSCs and the IGF inhibitors successfully masked AR mediated IGFBP3 signaling effects on pAkt expression in WT and ARKO BMSCs (Hashimoto et al, 1997; Oesterreicher et al, 2005; Wang et al, 2006; Xu et al, 1996) (Fig.4 H). Taken together, the results in Figure 4 clearly showed that knockout of AR suppressed IGFBP3 activation of Akt signaling and influenced the adipogenesis process.…”