Interactions of thrombospondin with endothelial cells: receptor-mediated binding and degradation.

Abstract

Abstract. We studied binding and degradation of labeled platelet thrombospondin (TSP) by normal and variant bovine aorta endothelial (BAE) cells.[125I]-labeled TSP bound to cells at 37~ in a specific, saturable, and time-dependent fashion. Incubation of cell monolayers with fluoresceinated TSP resulted in punctate cellular staining, but no staining of the extracellular matrix. Heparin, fucoidan, chondroitin sulfate, platelet factor 4, beta-thromboglobulin, unlabeled TSP, and serum derived from whole blood all competed for binding of [~25I]TSP. [12Sl]TSP was degraded to TCA-soluble radioactivity, which appeared in the medium after a 60-90-min lag. Degradation was inhibited to the same extent as binding by increasing concentrations of heparin, fucoidan, platelet factor 4, or whole blood serum. Normal BAE cells bound and degraded less [t2q]TSP than variant BAE cells. The dissociation constants (Kas) for binding and the constants for degradation (Kms) for degradation by the two cell strains, however, were similar (30-50 nM). The inhibitory effects of heparin and platelet factor 4 were lost when the two inhibitors were present in a 1:1 (wt/wt) ratio. Treatment of suspended cells with trypsin or heparitinase caused less binding of TSP. These results indicate that there is a specific receptor for TSP on endothelial cells which mediates binding and degradation. This receptor may be a heparan sulfate proteoglycan.

Cell biology of arterial proteoglycans.

“…138164 Thus, it may be that certain components of the extracellular matrix are necessary for cellular proliferation 167 and that other matrix components, such as proteoglycans, influence the availability of such molecules. The fact that cellassociated HSPG can serve as a receptor for thrombospondin 168 supports this possibility. It is also possible that heparin-like molecules regulate growth by interfering with the response to specific mitogens.…”

“…In addition, thrombospondin binds to the surface of vascular endothelial cells in a receptor-like fashion and this binding is inhibited by heparin, suggesting that thrombospondin associates with the surface of endothelial cells in a HSPG-dependent manner. 168 The importance of thrombospondin in regulating smooth muscle cell growth 164186 suggests a growth regulatory role for the HSPG present on the surface of smooth muscle cells. It remains to be determined whether thrombospondin associates with the surface of smooth muscle cells as it does with endothelial cells.…”

Processing of MIA protein during melanoma cell migration

“…In previous studies, it was reported that remodeling of matrix structures occurs via internalization of extracellular matrix proteins and degradation in lysosomes. [28][29][30][31] It was shown that-identical to MIA protein-turnover of extracellular matrix protein fibronectin is processed via integrin a 5 b 1 internalization. This endocytosis mechanism is constitutively regulated by caveolin-1 and can occur in presence or absence of fibronectin and fibronectin matrix.…”

Cellular Internalization and Degradation of Thrombospondin-1 Is Mediated by the Amino-terminal Heparin Binding Domain (HBD)

“…However, in contrast to LRP, the VLDL receptor is expressed in the endothelium (37,40). Since TSP-1 is catabolized by endothelial cells (41), it was of interest to determine if the VLDL receptor could mediate the cellular catabolism of TSP-1. For these experiments, an adenoviral vector was utilized to express the VLDL receptor in PEA-13 fibroblasts, a cell line that does not express this receptor or LRP.…”