Tissue Factor Encryption/de-encryption Is not Altered in the Absence of the Cytoplasmic Domain

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 (TF CD ). Comparison of intact cells (encrypted) with fully disrupted cells (de-encrypted) showed that TF and TF CD were equally encrypted with respect to function in fX activation. Moreover, cells expressing TF and TF CD 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.