The effects of the pleiotropic
serine protease thrombin on
tumor cells are commonly thought to be mediated by the
thrombin receptor protease-activated receptor 1 (PAR1). We demonstrate here that PAR1 activation has a role in experimental
metastasis using the anti-PAR1
antibodies ATAP2 and WEDE15, which block PAR1 cleavage and activation.
Thrombin also stimulates chemokinesis of human
melanoma cells toward fibroblast
conditioned media and soluble matrix
proteins.
Thrombin-enhanced migration is abolished by anti-PAR1
antibodies, demonstrating that PAR1 cleavage and activation are required. The PAR1-specific agonist
peptide TFLLRNPNDK, however, does not stimulate migration, indicating that PAR1 activation is not sufficient. In contrast, a combination of TFLLRNPNDK and the PAR2 agonist
peptide SLIGRL mimics the
thrombin effect on migration, whereas PAR2 agonist alone has no effect. Agonist
peptides for the
thrombin receptors PAR3 and PAR4 used alone or with PAR1 agonist also have no effect. Similarly, activation of PAR1 and PAR2 also enhances chemokinesis of
prostate cancer cells. Desensitization with PAR2 agonist abolishes
thrombin-enhanced cell motility, demonstrating that
thrombin acts through PAR2. PAR2 is cleaved by
proteases with
trypsin-like specificity but not by
thrombin.
Thrombin enhances migration in the presence of a cleavage-blocking anti-PAR2 antibody, suggesting that
thrombin activates PAR2 indirectly and independent of receptor cleavage. Treatment of
melanoma cells with
trypsin or PAR2 agonist
peptide enhances experimental
metastasis. Together, these data confirm a role for PAR1 in migration and
metastasis and demonstrate an unexpected role for PAR2 in
thrombin-dependent
tumor cell migration and in
metastasis.