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

Abstract

Sm_mary In this study we have investigated the role of thrombospondin (TSP) as a possible ligand playing a key role in human M3Da. melanoma cell interaction with platelets and in tumour growth. TSP is secreted (80 ± 6 ng TSP 1O-' cells) Keyword: thrombospondin; melanoma; monoclonal antibodies; platelet aggregation; vitronectin receptor Thrombospondin (TSP) is a high molecular weight (450 kDa) glycoprotein (GP) that is released from the a-granules of platelets during activation (Lawler, 1986). In the presence of a physiological concentration of calcium, TSP binds to the surface of stimulated platelets and plays an active role in promoting platelet aggregation (Leung, 1984;Boukerche and McGregor, 1988;McGregor and Boukerche, 1993 al., 1986, 1989). In addition to its role in blood coagulation, TSP has been reported to promote adhesion and motility of several of these cell types (Walz, 1992). 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. We have previously reported that a monoclonal antibody (LYP18), generated against human blood platelet glycoprotein lIb-Illa (muA), immunoprecipitated two proteins from a tumorigenic human melanoma cell line (M3Da.) immunologically related to the vitronectin receptor (a,3) (Boukerche et al., 1989a,b

Role of β3 Integrins in Melanoma Cell Adhesion to Activated Platelets under Flow

“…Failure of M21 cells to bind to adhered platelets in which the integrin ␣IIb␤3 function had been blocked suggests that ␣IIb␤3 participates in the interaction between platelets and melanoma cells. This concept is supported by previous reports (44,45) and is substantiated by the finding that platelets from Glanzmann's thrombasthenic patients, which lack ␣IIb␤3 expression, failed to interact with tumor cells in vitro (46). In order to identify a potential counter receptor for platelet integrin ␣IIb␤3 expressed by the melanoma cells, we reasoned that ␣IIb␤3 may bind to a related receptor expressed by the melanoma cell using a mechanism similar to that which governs platelet-platelet interaction in thrombus formation.…”

“…In order to identify a potential counter receptor for platelet integrin ␣IIb␤3 expressed by the melanoma cells, we reasoned that ␣IIb␤3 may bind to a related receptor expressed by the melanoma cell using a mechanism similar to that which governs platelet-platelet interaction in thrombus formation. Evidence suggests that an ␣IIb␤3-related integrin expressed by tumor cells might be involved in their interaction with platelets (46,47). This ␣IIb␤3-related molecule may represent tumor cell integrin ␣v␤3, since these receptors share characteristic homologies and a ligand recognition repertoire.…”

Loss-of-function thrombospondin-1 mutations in familial pulmonary hypertension

“…TSP1 levels of 10 nM appear to be at or above the dissociation constant (K d ) for known TSP1 receptors, with the K d of CD47 being the lowest at 12 pM (7,21). Thus the picomolar to low nanomolar concentrations of trimeric TSP1 that we tested are likely present in the unperturbed lung, relevant to early phases of PAH pathogenesis.…”

Role of PLZF in melanoma progression

“…Cell adhesion assays were performed essentially as described (Boukerche et al, 1995). Briefly 96-well flat-bottom microtiter plates were coated with 150 ng/cm 2 of matrigel and 50 or 200 ng/cm 2 of vitronectin for 2 h at 371C; melanoma cell lines were seeded at a density of 10 4 cells/well in 200 ml of serum-free DMEM containing 0.35% BSA.…”