Summary
Since the cytoplasmic domain of tissue factor (TF) appears to have a role in TF function
beyond coagulation, experiments were conducted to determine whether the cytoplasmic
domain also has a role in regulating procoagulant activity of TF present in the cell
membrane. TF encryption was quantitated in human YU-SIT1, U87-MG, and mouse 3T3 cells
which were transfected for expression of human tissue factor or a construct lacking
the cytoplasmic domain (TFCD). Comparison of intact cells (encrypted) with fully disrupted cells (de-encrypted)
showed that TF and TFCD were equally encrypted with respect to function in fX activation. Moreover, cells
expressing TF and TFCD were indistinguishable in their procoagulant responses to A23187-calcium and varied
concentrations of nonionic detergents. TF in membrane vesicles spontaneously shed
by U87-MG cells was largely, but incompletely, de-encrypted, and the degree of de-encryption
was independent of the cytoplasmic domain. We conclude that the predominant mechanism(s)
for encrypting TF procoagulant activity is independent of the cytoplasmic domain.
Key words
Tissue factor - encryption - cytoplasmic domain