Role of beta 3 integrins in melanoma cell adhesion to activated platelets under flow

Mechanisms mediating tumor cell attachment to the vessel wall under flow conditions are largely unknown, Therefore we analyzed the ability of human melanoma cells to adhere to an immobilized matrix during blood flow and determined the role of platelets in this process, In a parallel plate flow chamber, M21 melanoma cells were suspended in human blood and perfused over a collagen I matrix at a wall shear rate of 50 s(-1) (2 dynes/cm(2)) to simulate venous flow over a thrombogenic surface, Melanoma cell interaction with the matrix or blood cells and platelets was monitored and quantified by fluorescence and confocal laser microscopy, Despite their ability to adhere to collagen I under static conditions, M21 cells failed to attach directly to this matrix during blood flow, However, they associated with adherent thrombi, and this resulted in stable melanoma cell arrest, Inhibition of platelet activation or platelet integrin alpha IIb beta 3 function abolished M21 cell attachment, Melanoma cell interaction with thrombi was specific and required beta 3 integrin expression, M21-L cells which lack integrin alpha v beta 3 failed to associate with thrombi and to arrest during blood flow, Transfection of these cells with the integrin subunits alpha v or alpha IIb resulted in variants expressing alpha v beta 3, as in the wild type, or alpha IIb beta 3. Both variants were able to associate with thrombi and to arrest during blood flow, Therefore, beta 3 integrin-mediated binding to activated platelets represents an efficient mechanism for melanoma cell arrest under flow, and this may contribute to the role of platelets in hematogenous metastasis.