THROMBIN ENHANCES THE ADHESION AND MIGRATION OF HUMAN COLON ADENOCARCINOMA CELLS VIA INCREASED BETA(3),-INTEGRIN EXPRESSION ON THE TUMOR-CELL SURFACE AND THEIR INHIBITION BY THE SNAKE-VENOM PEPTIDE, RHODOSTOMIN

The interactions between tumour cells and the microvasculature, includ ing the adhesion of tumour cells to endothelium and extracellular matr ix (ECM) as well as their migratory ability, are prerequisites for met astasis to occur. In this study we showed that thrombin is capable of enhancing in vitro tumour cell metastatic potential in terms of adhesi ve properties and migratory response. Following exposure to subclottin g concentrations of thrombin, SW-480 human colon adenocarcinoma cells exhibited increased adhesion to both the endothelium and ECM component (i.e. fibronectin). Likewise, the pretreatment of thrombin enhanced t he migratory ability of SW-480 cells. The enhanced adhesion was signif icantly inhibited by complexing of thrombin with its inhibitor hirudin , or by serine proteinase inhibition with 3,4-DCI, but was unaffected by pretreatment of tumour cells with actinomycin D or cycloheximide. T he effect of thrombin resulted in an upregulated cell-surface expressi on of beta(3) integrins, a group of receptors mediating interactions b etween tumour cells and endothelial cells, and between tumour cells an d ECM. Antibodies against beta(3) integrins effectively blocked both t he enhanced adhesion and migration. This thrombin-mediated up-regulati on of beta(3) integrins involved the activation of protein kinase C (P KC) as thrombin-enhanced adhesion was diminished by PKC inhibition. Rh odostomin, an Arg-Gly-Asp-containing antiplatelet snake venom peptide that antagonises the binding of ECM toward beta(3) integrins on SW-480 cells, was about 600 and 500 times, more potent than RGDS in inhibiti ng thrombin-enhanced adhesion and migration respectively. Our data sug gest that PKC inhibitors as well as rhodostomin may serve as inhibitor y agents in the prevention of thrombin-enhanced metastasis.