Biological activities of peptides and peptide analogues derived from common sequences present in thrombospondin, properdin, and malarial proteins.

Abstract

Abstract. Thrombospondin (TSP), a major plateletsecreted protein, has recently been shown to have activity in tumor cell metastasis, cell adhesion, and platelet aggregation. The type 1 repeats of TSP contain two copies of CSVTCG and one copy of CSTSCG, per each of the three polypeptide chains of TSP and show homology with peptide sequences found in a number of other proteins including properdin, malarial circumsporozoite, and a blood-stage antigen of Plasmodium falciparum . To investigate whether these common sequences functioned as a cell adhesive domain in TSP, we assessed the effect of peptides corresponding to these sequences and an antibody raised against one of these sequences, CSTSCG, in three biological assays which depend, in part, on the cell adhesive activity of TSP These assays were TSP-dependent cell adhesion, T HROMBOSPONDIN (TSP)l is a 450,000-dalton glycoprotein secreted by platelets in response to such physiological activators as thrombin and collagen (9). TSP comprises 3% of the total platelet protein and 25% of the total platelet-secreted protein (26) . Although the precise biological role of TSP has yet to be fully established, it is generally accepted that TSP plays a major role in cell adhesion and cell-cell interactions . For example, TSP was found to promote the cell-substratum adhesion of a variety ofcells, including platelets, melanoma cells, muscle cells, endothelial cells, fibroblasts, and epithelial cells (24) . In addition, cells with very specialized functions such as keratinocytes (27) and osteoblasts (16) attach to TSP. Finally, TSP promotes the irreversible aggregation of platelets (23) .Thrombospondin has been postulated to play a role in malarial infection induced by only one strain of malaria, Plasmodiumfalciparum, and tumor cell metastasis induced by small cell carcinoma and mouse sarcoma. During malarial infection, TSP promotes adhesion of parasitized red cells to endothelial cells (15) and during tumor cell metastasis platelet aggregation, and tumor cell metastasis. We found that a number of peptides homologous to CSV TCG promoted the adhesion of a variety of cells including mouse B16-F10 melanoma cells, inhibited platelet aggregation and tumor cell metastasis, whereas control peptides had no effect . Anti-CSTSCG, which specifically recognized TSP, inhibited TSP-dependent cell adhesion, platelet aggregation, and tumor cell metastasis, whereas control IgG had no effect. These results suggest that CSVTCG and CSTSCG present in the type I repeats function in the adhesive interactions of TSP that mediate cell adhesion, platelet aggregation, and tumor cell metastasis. Peptides, based on the structure of these repeats, may find wide application in the treatment of thrombosis and in the prevention of cancer spread .TSP promotes adhesion of mouse sarcoma cells to the vascular bed (20) and expression of the malignant phenotype of small cell carcinoma (3). Furthermore, TSP has been shown to share sequence homologies with malarial circumsporozoite proteins (8), which function in the c...

Thrombospondin modulates melanoma-platelet interactions and melanoma tumour cell growth in vivo

“…Released TSP will bind to the surface of activated platelets or cells via a number of glycoprotein receptors, such as the integrins GPIIb-IIIa (oEA,) and m2p, Tuszynski and Kowalska, 1991), the vitronectin receptor a, (Lawler et al, 1988), GPIV (also called CD36) (Asch et al, 1987;McGregor et al, 1989), the integrin-like receptor (105/80 kDa) (Yabkowitz and Dixit, 1991) and the heparan sulphate proteoglycans (Roberts, 1988). Recently, it was shown that tumour formation and the metastatic spread of lung tumours in mice was increased by TSP and was significantly reduced by use of TSP peptide CSVTCG or a TSP cDNA antisense expression vector (Tuszynski et al, 1987(Tuszynski et al, , 1992Castle et al, 1991 However, so far very little is known about the precise biological role of TSP in tumour-platelet interactions and tumour cell growth. Moreover, the identity of the TSP receptor(s) mediating tumour cell-platelet interactions and tumour growth remains to be elucidated.…”

The role of angiocidin in sarcomas

“…Our laboratory and others have shown that TSP-1 up-regulates tumor-associated proteases and promotes tumor cell invasion and metastases in epithelial malignancies. 9,[15][16][17][25][26][27][28][29][30][31][32][33][34] We have recently shown that TSP-1 promotes tumor cell invasion in pancreatic and gastric cancer through a mechanism that involves up-regulation of gelatinases, 16,25,29,35 key enzymes in the metastatic cascade. 36,37 The potential role of TSP-1 in mesenchymal tumors such as sarcomas is presently unknown.…”

“…20,21 This recombinant CSVTCG peptide inhibits tumor cell invasion and decreases tumor metastasis in a mouse melanoma model. 17 The 25-mer peptide is derived from a 20 amino acid segment in the amino terminal domain of recombinant angiocidin. This particular domain of angiocidin contains the TSP-1 binding site; an angiocidin deletion mutant missing this domain fails to bind matrix proteins and loses its protumor effects.…”

“…Polyclonal antihuman TSP-1 antibody was raised in a goat as previously described. 17 Polyclonal antiangiocidin antibody was raised in a rabbit against angiocidin protein isolated from a human lung carcinoma and purified as previously described. 15 Sheep antihuman matrix metalloproteinase (MMP)-9 immunoglobulin G (IgG) was purchased from The Binding Site Co. (Birmingham, UK), and goat antihuman MMP-2 IgG was purchased from R&D Systems (Minneapolis, Minn).…”

Developmental Biology of Sporozoite-Host Interactions inPlasmodium falciparumMalaria: Implications for Vaccine Design

“…Some groups, using sequences derived from thrombospondin, have reached the conclusion that the CSVTCG segment is the motif responsible for cell adhesion activity (126). Work done by other groups with region II plus some peptides has revealed the importance of positively charged residues for CS binding to hepatocytes, suggesting that these residues interact with negatively charged proteoglycan glycosaminoglycan chains, while the CS VTCG sequence does not seem to play any role in this interaction (46).…”