Specific binding of basic fibroblast growth factor to basement membrane‐like structures and to purified heparan sulfate proteoglycan of the EHS tumor

Abstract

The binding of iodinated basic fibroblast growth factor (bFGF) to low‐density heparan sulfate proteoglycan purified from the Engelbreth Holm Swarm (EHS) sarcoma was investigated using different techniques. The tumor clearly contained bFGF, the level being comparable to that found in other tissues such as human or bovine brain. 125I bFGF strongly bound to the basement membrane‐like matrix of EHS frozen sections as revealed by autoradiography. Iodinated bFGF bound to purified heparan sulfate proteoglycan but not to laminin or collagen type IV, three components isolated from the same tumor. In contrast, acidic fibroblast growth factor (aFGF) displayed negligible binding to heparan sulfate proteoglycan. Binding of bFGF to frozen sections and to purified proteoglycan could be strongly inhibited by heparin and was displaced by an excess of unlabeled factor and completely suppressed after heparitinase and heparinase treatments. Binding was a function of the salt concentration and was abolished at 0.6 M NaCl. Scatchard analysis indicated the affinity site had a Kd of about 30 nM, a value 10–15 higher than that recently reported by Moscatelli (J. Cell. Physiol., 131:123–130, 1987) in the case of the low‐affinity binding sites present on the surface of baby hamster kidney (BHK) cells.

Fibroblast growth factors, their receptors and signaling.

“…Vlodavsky et al (1987) showed that endothelial cells synthesize FGF-2 which is then deposited and sequestered in the subendothelial ECM, a major component of which is heparan sulfate proteoglycan. It was also determined that this binding of FGF-2 to the basement membrane was specific to HLGAGs and not other basement membrane components such as laminin or collagen type IV (Vigny et al 1988). Folkman et al (1988) hypothesized that the interaction with heparin is representative of an in vivo affinity of FGFs for heparin sulfate proteoglycans, and furthermore, that the storage of FGFs in the basement membrane may be a mechanism for regulating their accessibility to vascular endothelium.…”

The Acidic Domain and First Immunoglobulin-Like Loop of Fibroblast Growth Factor Receptor 2 Modulate Downstream Signaling through Glycosaminoglycan Modification

“…It has been suggested that fibroblast growth factors (FGFs) are stored and protected from proteolytic degradation in the extracellular matrix and on the cell surface by interaction with heparan sulfate proteoglycans, which thereby serve as a reservoir of the growth factors (9,26,30,33,44,45). Heparan sulfate proteoglycans not only play such a modulatory role but are involved in the binding of FGF to its high-affinity receptors as an essential component.…”

Fibroblast Growth Factor-2 Can Mediate Cell Attachment by Linking Receptors and Heparan Sulfate Proteoglycans on Neighboring Cells

“…In addition to these regions defined by splicing variations, other regions of the extracellular portion of the FGF receptors that might have functional importance have been identified. These include (i) the acidic box, a sequence of four to eight contiguous acidic amino acids between the first and second immunoglobulin-like domains, (ii) a proposed heparin-binding domain within the second immunoglobulin-like domain (12), and (iii) a region between the first and second immunoglobulin-like domains that bears homology to the cadherin cell adhesion recognition sequence (13).FGF-2 also binds with lower affinity to the heparan sulfate moieties of proteoglycans on the cell surface and in the extracellular matrix (4,14,15). The binding of FGF-2 to heparan sulfates confers several biological advantages to the growth factor: (i) FGF-2 bound to heparin or heparan sulfates is protected from proteolysis and thermal denaturation (16,17); (ii) the heparan sulfate-bound FGF-2 serves as a reserve of growth factor that can support long term responses to FGF-2 after a…”

“…FGF-2 also binds with lower affinity to the heparan sulfate moieties of proteoglycans on the cell surface and in the extracellular matrix (4,14,15). The binding of FGF-2 to heparan sulfates confers several biological advantages to the growth factor: (i) FGF-2 bound to heparin or heparan sulfates is protected from proteolysis and thermal denaturation (16,17); (ii) the heparan sulfate-bound FGF-2 serves as a reserve of growth factor that can support long term responses to FGF-2 after a…”

“…FGF-2 also binds with lower affinity to the heparan sulfate moieties of proteoglycans on the cell surface and in the extracellular matrix (4,14,15). The binding of FGF-2 to heparan sulfates confers several biological advantages to the growth factor: (i) FGF-2 bound to heparin or heparan sulfates is protected from proteolysis and thermal denaturation (16,17); (ii) the heparan sulfate-bound FGF-2 serves as a reserve of growth factor that can support long term responses to FGF-2 after a brief exposure to the growth factor (18,19); (iii) the heparan sulfates of the tissues may provide a means to localize FGF-2 to a particular site, limiting its diffusion (20); (iv) soluble heparan sulfates can act as carriers of FGF-2 and by preventing its interaction with fixed heparan sulfates in the tissues assure its dissemination away from its site of release (20); (v) FGF-2 can be internalized through its interaction with cell-surface heparan sulfates, clearing excess active molecules from the cell surface, perhaps helping to dampen the response to FGF-2 (21-23); and (vi) heparin or heparan sulfates can increase the affinity of FGF-2 for its receptors, by decreasing the dissociation rate of the FGF-2-receptor complex (24 -26).…”