Norstrøm Eva, Thorelli Elisabeth, Dahlbäck Björn
Department of Clinical Chemistry, Division of Laboratory Medicine, Lund University, University Hospital Malmö, Sweden.
Blood. 2002 Jul 15;100(2):524-30. doi: 10.1182/blood-2002-02-0343.
In factor V (FV) Cambridge (Arg306Thr) and Hong Kong (Arg306Gly), a cleavage site for anticoagulant activated protein C (APC), which is crucial for the inactivation of FVa, is lost. Although patients carrying FV Hong Kong have a normal APC response, those with FV Cambridge were reported to be APC resistant. To elucidate the molecular characteristics of the 2 FV mutants, we recreated them in a recombinant system and evaluated their functional properties. The 2 FV variants yielded identical APC resistance patterns, with APC responses being intermediate to those of wild-type FV and FV Leiden (Arg506Gln), which is known to be associated with the APC resistance phenotype. In the absence of protein S, APC mediated FVa inactivation curves obtained with the 2 variants were identical, resulting in partial FVa inactivation. In the presence of protein S, both FVa variants were almost completely inactivated because of protein S stimulation of the cleavage at Arg679. In a FVIIIa degradation system, both FV variants demonstrated slightly impaired APC cofactor activity. The ability of APC to cleave at Arg506 and at Arg679 in FVa Cambridge and Hong Kong and the slight decrease in APC cofactor activity of the 2 FV variants may explain the low thrombotic risk associated with these Arg306 mutations. In conclusion, we demonstrate that recombinant FV Cambridge and Hong Kong behave identically in in vitro assays and provide a mechanism for the low thrombotic risk associated with these FV mutations.
在因子V（FV）剑桥型（Arg306Thr）和香港型（Arg306Gly）中，抗凝血活化蛋白C（APC）的一个裂解位点丢失，该位点对于FV a的失活至关重要。尽管携带FV香港型的患者APC反应正常，但据报道携带FV剑桥型的患者对APC耐药。为了阐明这两种FV突变体的分子特征，我们在重组系统中重新构建了它们并评估了其功能特性。这两种FV变体产生相同的APC耐药模式，其APC反应介于野生型FV和FV莱顿型（Arg506Gln）之间，已知FV莱顿型与APC耐药表型相关。在没有蛋白S的情况下，用这两种变体获得的APC介导的FV a失活曲线相同，导致FV a部分失活。在有蛋白S的情况下，由于蛋白S刺激Arg679处的裂解，两种FV a变体几乎完全失活。在FVIII a降解系统中，两种FV变体均表现出APC辅因子活性略有受损。APC在FV剑桥型和香港型的Arg506和Arg679处的裂解能力以及这两种FV变体的APC辅因子活性略有降低，可能解释了与这些Arg306突变相关的低血栓形成风险。总之，我们证明重组FV剑桥型和香港型在体外试验中的行为相同，并为与这些FV突变相关的低血栓形成风险提供了一种机制。
