H. Boukerche et al., THROMBOSPONDIN MODULATES MELANOMA-PLATELET INTERACTIONS AND MELANOMA TUMOR-CELL GROWTH IN-VIVO, British Journal of Cancer, 72(1), 1995, pp. 108-116
In this study we have investigated the role of thrombospondin (TSP) as
a possible ligand playing a key role in human M(3)Da. melanoma cell i
nteraction with platelets and in tumour growth. TSP is secreted (80 +/
- 6 ng TSP 10(-6) cells) and bound to the surface of M(3)Da. cells via
receptors different from CD36, as shown by biosynthetic labelling and
immunofluorescence studies. The levels of TSP binding to M(3)Da. cell
s evaluated by binding studies, using an anti-TSP monoclonal antibody
(MAb) (LYP8), shows 367 000 +/- 58 000 (mean +/- s.d.) LYP8 binding si
tes per cell with a dissociation constant (K-d) of 67 nM. TSP binding
to M(3)Da. cells shows 400 000 +/- 50 000 TSP binding sites per cell w
ith a K-d Of 10 nM. The capacity of anti-TSP MAb (LYP8) to inhibit M(3
)Da.-platelet interactions was followed on an aggregometer and evaluat
ed by electron microscopy studies. Toe biological role of TSP binding
to M(3)Da. cells was investigated by implanting subcutaneously the M(3
)Da. cell line in nude mice and following the size and time of in vivo
tumour growth. Reducing the availability or the functional level of T
SP by using an anti-TSP MAb (LYP8) resulted in a significant decrease
in platelet aggregates interacting with M(3)Da. melanoma cells. Using
an enzyme-linked immunosorbent assay, purified alpha(v) beta(3) was sh
own to bind TSP. Moreover, LYP8-coated M(3)Da. cells showed a reduced
capacity to form rumours in vivo. M(3)Da. cells were observed to attac
h and spread on human platelet TSP-coated plastic wells. This attachme
nt by M(3)Da. cells was inhibited in a similar way by LYP8 and an anti
-alpha(v) beta(3) MAb (LYP18). The results obtained in this study show
that TSP secreted and bound to the surface of a human melanoma cell l
ine (M(3)Da.) acts as a link between aggregated platelets and the M(3)
Da. cell surface. Moreover, these results shows that TSP can modulate
tumour growth in vivo. Reagents such as MAbs directed against TSP and
peptides derived from TSP could not only be used as a new therapeutic
approach in the control of tumour metastasis of melanoma, but may also
contribute to elucidation of the role of TSP in cancer biology.