Active site blockade of factor VIIa alters its intracellular distribution

Factor VIIa binding to tissue factor on cell surfaces not only triggers the coagulation cascade but also induces various intracellular responses that may contribute to many pathophysiological processes. Active site-inhibited factor VIIa, similar to factor VIIa, binds to tissue factor on cell surface s and subsequently gets internalized and degraded. At present, it is unknow n whether factor VIIa and active site-inhibited factor VIIa undergo a simil ar intracellular processing. The data presented herein show that although a fraction of both the internalized factor VIIa and active site-inhibited fa ctor VIIa recycle back to the cell surface, the amount of active site-inhib ited factor VIIa recycled back to the cell surface was substantially higher than that of factor VIIa. Furthermore, internalized factor VIIa and not ac tive site-inhibited factor VIIa associates with nuclear fractions. Factor V IIa associated with the nuclear fraction was intact and functionally active . In contrast to factor VIIa, tissue factor is not found in the nuclear fra ction. Additional studies show that the internalized factor VIIa specifical ly associates with cytoskeletal proteins, actin, and tubulin. In summary, t he present data reveal that despite the common pathway of tissue factor-med iated processing, considerable differences exist in the trafficking of fact or VIIa and active site-inhibited factor VIIa in fibroblasts.