The GPIIB-IIIa-like complex may function as a human melanoma cell adhesion receptor for thrombospondin.

The purpose of this study was to determine whether a heterodimeric complex immunologically related to the fibrinogen receptor could function as a thrombospondin (TSP) receptor in TSP-mediated cell-substratum adhesion of human melanoma cells. We found that polyclonal antibodies to the platelet GPIIb-IIIa complex, GPIIIa, and the human vitronectin receptor inhibited TSP-mediated cell adhesion by 63-68%. Immunoprecipitation of detergent extracts of 125I-surface-labeled melanoma cells using either anti-human platelet GPIIb-IIIa or anti-human vitronectin receptor antibody revealed the presence of a single heterodimeric complex, suggesting that both antisera recognize the same integrin receptor, GPIIb-IIIa-like antigen. Adhesion of cells to TSP is likely mediated through a region of the TSP molecule containing the arginine-glycine-aspartic (RGD) peptide sequence, since cell attachment to TSP was inhibited 50-66% in the presence of peptides containing RGD. These results strongly suggest that a GPIIb-IIIa-like/vitronectin receptor can serve as a cell binding site for TSP in mediating cell-substratum adhesion.