Flow modulation of receptor-mediated interactions in inflammation and cancer metastasis

Intercellular adhesion plays a pivotal role in numerous diverse biological processes that occur within the vasculature, ranging from inflammation to cancer metastasis. Several lines of evidence suggest that enhanced leukocyte-platelet adhesion occurs in the circulation of patients with acute myocardial infraction or stroke. Furthermore, accumulating data implicates that successful metastatic spread is dependent upon tumor cells adhesive interactions with platelets. While the involvement of platelets in these patho-physiological phenomena has been demonstrated, the kinetics and molecular constituents that govern these adhesive interactions under shear remains largely unknown. Therefore, this study was undertaken to elucidate the mechanisms that mediate both immune and tumor cell adhesion to platelets.; A parallel-plate flow chamber coupled with phase-contrast microscopy was utilized to characterize the binding of eosinophils to immobilized platelets under shear. Using this technique, eosinophil P-selectin-glycoprotein-ligand-1 (PSGL-1) was shown to mediate tethering to platelet P-selectin, while exogenous activation of eosinophils was shown to convert PSGL-1 binding to CD18-dependent stable adhesion to platelets. This methodology was then extended to show that surface-anchored platelets support human colon carcinoma LS174T cell binding primarily through a sequential process of adhesive interactions. The involvement of platelet P-selectin is requisite for the efficient tethering of free-flowing colon carcinomas in shear flow, thereby allowing platelet α_IIb β₃-integrins to engage and convert these tethering interactions into firm adhesion.; In an effort to study tumor cell-platelet interactions in a more physiologically relevant environment, cell suspensions were subjected to a uniform shear field using a cone-and-plate rheometer. The results indicate that hydrodynamic shear-induced collisions augment platelet-LS174T cell binding. Moreover, fluid shear affects the receptor specificity of platelet binding to LS174T cells, as evidenced by the transition from a P-selectin-independent process at 100 sec−1 to a P-selectin/α_IIbβ ₃ integrin-dependent interactions at 800 sec−1.; To further characterize the biophysical properties of the unknown P-selectin ligand(s) present on the LS174T cell surface, a molecular force probe was utilized to quantify the de-adhesion forces and dissociation constant associated with individual P-selectin/ligand complexes.; Collectively, these findings may provide insights for the rational development of novel therapeutics to effectively combat cellular processes such as inflammation and cancer metastasis.