The interactions between tumour cells and the microvasculature, including the adhesion of tumour cells to endothelium and extracellular matrix (ECM) as well as their migratory ability, are prerequisites for
metastasis to occur. In this study we showed that
thrombin is capable of enhancing in vitro tumour cell metastatic potential in terms of adhesive properties and migratory response. Following exposure to subclotting 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 the migratory ability of SW-480 cells. The enhanced adhesion was significantly 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. The effect of
thrombin resulted in an upregulated cell-surface expression of beta 3
integrins, a group of receptors mediating interactions between tumour cells and endothelial cells, and between tumour cells and ECM.
Antibodies against beta 3
integrins effectively blocked both the enhanced adhesion and migration. This
thrombin-mediated up-regulation of beta 3
integrins involved the activation of
protein kinase C (PKC) as
thrombin-enhanced adhesion was diminished by PKC inhibition.
Rhodostomin, 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 that RGDS in inhibiting
thrombin-enhanced adhesion and migration respectively. Our data suggest that PKC inhibitors as well as
rhodostomin may serve as inhibitory agents in the prevention of
thrombin-enhanced
metastasis.