ROLE OF BETA-3 INTEGRINS IN MELANOMA CELL-ADHESION TO ACTIVATED PLATELETS UNDER FLOW

Mechanisms mediating tumor cell attachment to the vessel wall under fl ow conditions are largely unknown, Therefore we analyzed the ability o f human melanoma cells to adhere to an immobilized matrix during blood flow and determined the role of platelets in this process, In a paral lel plate flow chamber, M21 melanoma cells were suspended in human blo od 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 surfac e, Melanoma cell interaction with the matrix or blood cells and platel ets was monitored and quantified by fluorescence and confocal laser mi croscopy, Despite their ability to adhere to collagen I under static c onditions, M21 cells failed to attach directly to this matrix during b lood flow, However, they associated with adherent thrombi, and this re sulted in stable melanoma cell arrest, Inhibition of platelet activati on or platelet integrin alpha IIb beta 3 function abolished M21 cell a ttachment, Melanoma cell interaction with thrombi was specific and req uired beta 3 integrin expression, M21-L cells which lack integrin alph a 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 integr in-mediated binding to activated platelets represents an efficient mec hanism for melanoma cell arrest under flow, and this may contribute to the role of platelets in hematogenous metastasis.