A number of studies indicate that coagulation
proteases play significant roles in
cancer biology.
Melanoma is a highly metastatic
cancer, and there is evidence that
thrombin contributes to this aggressive pattern. However, few studies correlate this type of
cancer with formation of the
prothrombinase complex, which is responsible for conversion of
prothrombin into
thrombin in the coagulation system. The aim of this study was to investigate the assembly and regulation of
prothrombinase complex on the murine
melanoma cell line, B16F10. B16F10 cells were unable to activate
prothrombin except when previously incubated with
factor Xa. This effect was dependent on
factor Xa binding to cell membranes, since no activation was detected with Gla-domainless
factor Xa. The
thrombin formation by B16F10-bound
factor Xa was enhanced approximately 10 fold in the presence of
factor Va, indicating the assembly of
prothrombinase complex. Differently from platelets, B16F10-assembled
prothrombinase complex was inhibited by
prothrombin fragment 1 but not by fragment 2. In addition,
bothrojaracin, a specific
ligand of proexosite I on
prothrombin, caused a significant decrease in the
zymogen activation. Our data demonstrate that B16F10
melanoma cells generate
thrombin by promoting assembly of the
prothrombinase complex. This ability might be correlated with the increased metastatic potential of this cell line. Moreover, B16F10-assembled
prothrombinase complex seems to be modulated in a different way from that found for the physiological complex assembled on platelets.