Background: Coagulation factor V (FV) has pro-coagulant and anticoagulant functions. We reported that the FV-W1920R mutation (FV-NARA) in a patient with deep vein thrombosis and were resistant to APC (Nogami et al. Blood 2014). However, this mutation was present in the C1 domain, which is remote from the cleavage sites of APC, and the mechanism(s) in which FV-W1920R caused APC resistance remains unknown.

Aims:  To elucidate the mechanism(s) of APC resistance in FV-W1920R.

Methods: We constructed HEK293 cells that express full-length FV stably using PiggyBac transposon. We evaluated the direct binding of FV to active-site blocked EGR-APC and PS by a surface plasmon resonance (SPR)-based assay.　And we compared the cleavage and inactivation rates by APC using FV-WT and FV-W1920R in the presence and absence of PS. To investigate the effect of APC, PS, and phospholipids, APC-mediated inactivation of FV was compared using various concentrations of them.

Results: SPR-based assay revealed that FV-W1920R (Kd 12.8 nM) showed similar binding affinity to FV-WT (Kd 10.7 nM) for EGR-APC. And FV-W1920R (Kd 15.3 nM) and FV-WT (Kd 7.56 nM) showed little differences in binding affinity for PS. In FV-WT, cleavage of Arg306 was confirmed only in the presence of PS, but in FV-W1920R, cleavage of Arg306 was not observed, irrespective of the presence of protein S. In FV-WT, the inactivation rate by APC was enhanced by the presence of PS, whilst in FV-Nara, the enhancement effect by PS was not observed, even in high concentration of PS.

Conclusions: The APC resistance in FV-W1920R was caused by the defective association between mutated FV molecule and PS in the PS/APC/FVa assembly

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/activated-protein-c-apc-resistance-in-fv-w1920r-fv-nara-was-caused-by-the-defective-association-between-fv-w1920r-and-protein-s-ps-in-the-apc-ps-fva-assembly/