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

Abstract

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 ␣IIb␤3 function abolished M21 cell attachment. Melanoma cell interaction with thrombi was specific and required ␤3 integrin expression. M21-L cells which lack integrin ␣v␤3 failed to associate with thrombi and to arrest during blood flow. Transfection of these cells with the integrin subunits ␣v or ␣IIb resulted in variants expressing ␣v␤3, as in the wild type, or ␣IIb␤3. Both variants were able to associate with thrombi and to arrest during blood flow. Therefore, ␤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.

Activated integrin αvβ3 cooperates with metalloproteinase MMP-9 in regulating migration of metastatic breast cancer cells

“…Expression of activated ␣v␤3 promotes tumor cell arrest during blood flow and causes a drastic increase in metastatic activity (9,15,23). Integrin activation modulates ligand recognition, cell migration, and invasion (6,7,(24)(25)(26) and endows tumor cells with crucial functions that permit or facilitate a disseminating phenotype.…”

“…To analyze a clinical significance of ␣v␤3 activation, we established primary metastatic cells from blood samples of stage IV breast cancer patients. These cells express integrin ␣v␤3 in an activated functional form as the receptor supports tumor cell arrest during blood flow (9,23). In these cell models, ␣v␤3 activation caused enhanced breast cancer cell migration toward fibronectin (9), vitronectin, and fibrinogen.…”

Platelet-induced enhancement of LS174T colon carcinoma and THP-1 monocytoid cell adhesion to vascular endothelium under flow

“…For example, earlier studies examining the role of nonexogenously stimulated platelets in tumor cell adhesion to ECM components under flow conditions did not indicate secondary tethering as a possible adhesion pathway. Rather, tumor cells were often found in large platelet or platelet-leukocyte thrombi (13,14), in which platelets deposited on ECM proteins supported firm adhesion of the cancerous cells (13,14). Without platelets, the tumor cells were unable to attach to the ECM proteins under consideration.…”

“…Neither of these investigations identified a role for platelets in mediating secondary tethering whereby a platelet transiently bridges an endothelium-adherent with a free-flowing leukocyte before the latter attaches to the endothelial surface. Similarly, platelet-tumor cell perfusions over components of the extracellular matrix (ECM) indicate an important role for platelets in promotion of tumor cell adhesion by bridging tumor cells to the ECM, yet secondary tethering was not evaluated (9,13,14).…”

“…It is believed that platelets provide a protective shield against cytotoxic immune cells (32) and facilitate tumor cell extravasation by potentiating tumor cell adhesive interactions with ECM proteins of the vessel wall (9,13). Morphological observations of tumor cells arrested in capillaries (24) and in lung microvasculature (4) revealed the close association of tumor cells with activated platelets.…”