Thrombospondin 1 as a scavenger for matrix-associated fibroblast growth factor 2

Abstract

The antiangiogenic factor thrombospondin 1 (TSP-1) binds with high affinity to several heparin-binding angiogenic factors, including fibroblast growth factor 2 (FGF-2), vascular endothelial growth factor (VEGF), and hepatocyte growth factor/ scatter factor (HGF/SF). The aim of this study was to investigate whether TSP-1 affects FGF-2 association with the extracellular matrix (ECM) and its bioavailability. TSP-1 prevented the binding of free FGF-2 to endothelial cell ECM. It also IntroductionAngiogenesis, sprouting of new blood vessels from pre-existing ones, is a crucial event in physiologic and pathologic processes, including tumor growth and metastasis. 1 Angiogenesis is a complex process, regulated by pro-and antiangiogenic factors, that involves dynamic interaction between a variety of cells, growth factors, and the extracellular matrix (ECM). 2 As in other morphogenic processes, the ECM acts not just as a structural support, but also as a direct modulator of cellular functions. Matrix components and bioactive fragments released by limited proteolysis can directly regulate endothelial cell functions. 3 In addition, the matrix contributes to angiogenesis by acting as a reservoir for angiogenic factors. Growth factors are stored in the matrix through binding to heparansulfate proteoglycans (HSPGs). Binding to HSPGs is reversible, 4 and biologically active factors can be released from the matrix by different agents. 5,6 Fibroblast growth factor 2 (FGF-2, basic FGF) is the most extensively studied example of matrix-stored angiogenic factor. 5,7 As do other members of the FGF family, FGF-2 has a high affinity for the glycosaminoglycan heparin and for HSPGs. Cell-surface HSPGs are required for the formation of an active FGF/FGF receptor signaling complex, 8 for internalization, and hence for internalization-dependent activities such as endothelial cell proliferation. 7,9 Conversely, matrix-associated HSPGs allow the storage of FGF-2 within the ECM. 10 Matrix-associated FGF-2 can then act locally, or be released as a soluble, biologically active factor. 6 Mobilization of active FGF-2 from the matrix is an important mechanism of induction of angiogenesis. Biologically active FGF-2 is released by heparin, 11 matrix-degrading proteases, 12 heparanase, 13 and the FGF-binding protein (FGF-BP). 14 Conversely, other endogenous or pharmacologic agents that prevent FGF-2 interaction with HSPGs exert an antiangiogenic activity, as in the case of platelet factor 4 (PF-4), 15 a soluble syndecan ectodomain, 16 suramin, 17 chemically modified heparins, and heparin-mimicking polyanionic compounds. [18][19][20] Other important angiogenic factors, including vascular endothelial growth factor (VEGF) and hepatocyte growth factor/scatter factor (HGF/SF), bind to HSPGs that again contribute to growth factor binding to cell receptors and to the ECM. [21][22][23] Thrombospondin 1 (TSP-1) is the most studied member of a family of at least 5 related proteins. 24,25 TSP-1 is a matricellular molecule, a modular glycoprotein composed of mult...

Antiangiogenic activity of trabectedin in myxoid liposarcoma: Involvement of host TIMP‐1 and TIMP‐2 and tumor thrombospondin‐1

“…It acts through multiple mechanisms, including direct interaction with endothelial cell receptors and sequestration of angiogenic factors and proteases. [26][27][28][29][30] TSP-1 is a critical determinant of angiogenesis, dormancy and growth in different types of sarcomas. [18][19][20]31 In agreement with this suppressive activity, TSP-1 expression is downregulated in highly vascularized sarcomas, including myxoid liposarcoma, [17][18][19] and its induced expression impairs the in vivo growth of Ewing's sarcoma models.…”

Physical contact with endothelial cells through 1- and 2- integrins rescues chronic lymphocytic leukemia cells from spontaneous and drug-induced apoptosis and induces a peculiar gene expression profile in leukemic cells

“…33 In contrast with the reported decrease of THBS-1 in CLL cells adhering to stromal cells, we found that CLL cells, when cocultured on an endothelial layer, up-regulated THBS-1. Classically considered an anti-angiogenic factor, 34 THBS-1 can also be considered a stimulator of tumor progression and angiogenesis by inducing proteolytic degradation of the extracellular matrix, cell migration and invasion through regulation of the plasminogen/plasmin system, up-regulation of MMP9 and activation of TGF-b1. 35 Of interest, CLL cells were reported to secrete THBS-1 and to express the thrombospondin receptor CD36.…”

Critical Role of Endogenous Thrombospondin-1 in Preventing Expansion of Healing Myocardial Infarcts

“…A recent study demonstrated that TSP-1 promotes the mobilization of matrix-bound FGF-2, generating an inactive TSP-1/FGF-2 complex, thus decreasing bioavailability of the growth factor. 32 In addition, TSP-1 is a potent inhibitor of …”